Drone files raise new questions of evidence destruction in Vallejo police killing of Sean Monterrosa

by Brian Krans | May 26, 2021

VALLEJO – On June 2, 2020, Vallejo police Detective Jarrett Tonn fired his rifle five times from the back seat of an unmarked police truck as it pulled up to a Walgreens pharmacy, hitting Sean Monterrosa once in the back of the head, according to his official autopsy report.

Officers were responding to reports of widespread looting that had swept the region amid protests over the police murder of George Floyd in Minneapolis a week earlier.

Seconds before Tonn fired, Capt. Lee Horton announced over the radio that “it looks like they’re armed, possibly armed.” Monterrosa had a roofing hammer in the front pocket of his black hoodie. Minutes before, according to video released by Vallejo police, the 22-year-old had been using that hammer to try to pry open a locker in the pharmacy, as others had tried to do earlier in the night. 

The video of Monterrosa in Walgreens is the only visual evidence the Vallejo Police Department has made public that shows Monterrosa in the final moments of his life. Police body cameras were obscured by vehicle seats and dashboards, as they were just arriving on the scene as Tonn started firing.

Coincidentally, a Medic Ambulance supervisor was reportedly flying a high-end drone in the area that an expert describes as “idiot proof.” But attorneys once representing the Monterrosa family in a civil rights and wrongful death lawsuit alleged early on that the drone had been “destroyed.” 

In the following days, two lieutenants were placed on leave for allegedly destroying the windshield of the truck that Tonn fired through. The California Department of Justice investigated the allegations and said that it turned its file over in late January to the Solano County District Attorney’s office, which has recused itself from the Monterrosa case. 

Newly available files related to Monterrosa’s killing obtained by JohnGlidden.com provide more insight into the investigation of it but raise new questions about what happened to any footage captured by the drone. 

A forensic specialist with the U.S. Secret Service was unable to pull any data from the DJI Mavic 2 Pro drone that was at the scene, including its internal and independent “black box” memory storage that automatically records detailed information about the device’s flight path, including stills from any video that was recorded. 

“If that is not there, you have serious problems,” said Werner von Stein, owner of the SF Drone School Research Center on Treasure Island and regular user of the Mavic 2. “There’s something fishy going on here.”

‘The most extraordinary incidence of lawless criminal behavior’

Monterrosa was declared dead at 1:31 a.m. on June 2, 2020, about an hour after a call went out to emergency responders about an “officer-involved shooting” at the Walgreens on Redwood Street. One of Tonn’s bullets struck Monterrosa in the base of his skull, leaving him with just a few minutes to live, according to the Solano County Sheriff’s forensic pathologist’s report. 

Moneterrosa’s body was removed from the scene and transported by Medic Ambulance to Kaiser Hospital in Vallejo. 

Medic Ambulance would send Monterrosa — who was dead before they transported him — a bill for $3,244.85.

Since dusk, Vallejo had been besieged with cars full of people breaking into various businesses around the city. 

Napa County Sheriff’s Office Deputy Joshua Coleman — a former Vallejo police officer involved in multiple shootings himself — responded to Vallejo to see “the most extraordinary incidence of lawless criminal behavior that I have ever witnessed in my entire 14 year career.”

Coleman wrote that he was concerned after hearing several gun stores had been attacked in the previous few days. “I could hear passerby residents yelling violent threats at the officers on every scene,” he wrote. “It was a very dangerous and volatile situation; I was keenly aware of the likelihood that officers could encounter armed burglars.”

The city of Vallejo’s first response to the events reflected how the business community was impacted. At a press conference the day after Monterrosa was killed, City Manager Greg Nyhoff described the groups entering the city as “packs.” The city would request help from the National Guard after someone lit a fire at City Hall.  

City officials refused to discuss the shooting of Monterrosa that day. In fact, Vallejo Police Chief Shawny Williams waited 38.5 hours to report the shooting had been fatal, despite pledging transparency after being sworn in as the city’s first Black police chief months before. 

Williams initially described Monterrosa’s stature as being on his knees with his hands above his waist. He also listed criminal charges associated with Monterrosa’s name, though Monterrosa had not been convicted of any of them. Vallejo police started gathering that information following his death.

Hours after his death, Monterrosa’s sisters contacted the Solano County coroner’s office to learn their brother was dead. Meanwhile, Vallejo Police Assistant Allen Pigg sent a handwritten fax to San Francisco police, asking for “all police reports in your possession regarding Sean Monterrosa.”

While Vallejo police portrayed Monterrosa as a criminal, the Vallejo Police Officers Association quickly filed legal actions against the city from releasing Tonn’s name, citing fears for his and his family’s safety. Despite the fact that his name was quickly made public in local news reports and eventually The New Yorker,  nearly a year later, the department has yet to officially release it. Department-released body camera footage of the shooting blurred his face and any mention of his name.

But reports from the San Mateo County Forensics Laboratory obtained by JohnGlidden.com lists “Officer Tonn” as the victim in the investigation surrounding Monterrosa’s death. Tonn was involved in three shootings since 2014, though Monterrosa was the first that was fatal.

Vallejo police regularly list themselves as the victims in use-of-force reports. 

‘The video files of interest had no content’

Solano County District Attorney’s Investigator Charles Renfro was one of several investigators on the scene after Monterrosa was shot. Renfro and Vallejo Detective Terry Schillinger contacted William “Billy’” White, an operations manager for Medic Ambulance who was flying a drone over the Walgreens “at or around” the time of the burglaries, according to Renfro’s report. 

Noting that Schillinger left a voicemail message for White to call him back, Renfro also interviewed a resident in the area who said she “observed a drone flying around the Walgreens just before the [officer-involved shooting],” his report states. 

For other details, Renfro pointed other investigators to reports from Schillinger, but those reports have not yet been made public. 

According to White’s claim for reimbursement with the city, the drone was confiscated at Medic Ambulance’s office in Vallejo, which is on the same block as the Walgreens. White wrote he had “reported [the] event to Capt. [Jason] Potts” and he had been “working” with Detective Jason Scott. The city reimbursed White $2,499.76 for his equipment on July 28. 

Reached by phone Tuesday, White said it would be “completely inappropriate” to comment about what happened with his drone. 

Nine days after Tonn killed Monterossa — Steven Baskerville, a Secret Service agent working at the National Computer Forensics Institute Lab at the University of Tulsa in Oklahoma received a DJI Mavic 2 Pro drone, controller, and seventh-generation iPad from Detective Kevin Rose of the Vallejo Police Department and Andre Charles, chief investigator at the Solano County District Attorney’s Office. 

Baskerville wrote in his final report to Vallejo police that he hooked the devices up to various data-retrieving programs, like Cellebrite, DataPilot, Forensic Toolkit, and HxD, but his searches weren’t fruitful. 

“The recovered video files from the external flash media were corrupt and unreadable. Additionally, the video files of interest had no content,” Baskerville wrote in his report. 

Baskerville found an MP4 file created on June 2 on the SD card, but the file’s internal data had been “overwritten” with zeros. All files from that day, he found, “contained no data.” Baskerville wrote that after “further research” he found that DJI drones can “overwrite” when they’re “improperly shutdown.”

That, to von Stein, seems odd. “It’s electronic. It can happen, but it’s not the norm. It’s rare,” he said. “That sounds like it was wiped.”

Brittany K. Jackson, Vallejo police’s public information officer, said the drone was handled within department policy and chain of custody was followed. 

“The VPD made several attempts to try and recover the information [from the drone],” Jackson said over email. “We were not able to recover the information, so we sent it to the agency experts at the Secret Service for possible data recovery by personnel trained to recover lost or corrupted data.”

As noted in the Secret Service report, “all files on the drone and the iPad were unreadable,” Jackson said, despite Vallejo police expecting “the drone to work and for its memory to contain supporting evidence.”

Werner von Stein, owner of the SF Drone School Research Center runs experiments on a DJI Mavic 2 drone, the same model that reportedly recorded video around the time of Sean Monterrosa’s death. (Courtesy Brian Krans)

Von Stein’s office is tucked in a corner of a former military building on Treasure Island. His specialty is aerial photography for map-making, which began with physical film and radio-controlled airplanes made of paper and balsa wood. He now handles much more sophisticated, yet user-friendly, drones for entities like the city of San Francisco.

DJI is the largest drone maker and considers the Mavic 2 to be its flagship consumer drone. It’s consistently one of the top-rated drones on the market. “It’s idiot-proof,” von Stein said. 

The Mavic wouldn’t likely get that kind of praise if it had the major design flaw of erasing or overwriting a video file if the device was shut down improperly. Its hardware and software are designed to keep the drones from running into something and crashing, including automatically returning when battery levels become critically low. 

While Baskerville’s report doesn’t say how the Mavic was improperly shutdown, von Stein theorized it could have been due to user error by pulling out the SD card or battery before stopping a recording. That could corrupt all the files on a card, but that’s where DJI’s software comes in. 

Even if a file on the removable SD card is corrupted, von Stein said a Mavic’s “black box” — which begins recording every time a Mavic drone takes off — shouldn’t be affected. 

Werner von Stein, owner of the SF Drone School Research Center, explains the details contained in what a “black box” on a DJI Mavic 2 drone records. (Brian Krans)

“The black box is independent of the SD card,” he said. “If that is not there, you have a serious problem.”

Besides the flight pattern, the drone’s black box records numerous data points, including when and where video recording started and stopped, as well as the direction of the camera and pictures of what’s on screen. That means the drone should have records of whether it captured video of Tonn shooting Monterossa, if it was recording and in-frame at the time.

To affect any of the Mavic 2’s black box recordings, a device must be physically connected via micro USB cable to the physical device. 

Werner von Stein, owner of the SF Drone School Research Center, shows off an example of what an iPad connected to a DJI Mavic 2 drone would internally record while in flight. (Brian Krans)

But flight records, as well as any recorded video, are also normally saved in the DJI Go app, which should have been on the iPad submitted to the Secret Service, von Stein said. 

“This is all independent. It technically should be there,” he said, adding he’s never personally experienced data disappearing like that in a DJI drone. 

Even if the video wasn’t saved, the drone operator would have seen what the drone’s camera was capturing in real time. Von Stein says no drone pilots fly without paying attention to what’s on screen. 

All told, Baskerville’s report says he was unable to pull any video files from the removable 128GB micro SD card, the drone’s internal memory or from the 128GB iPad. Nothing was readable, even with some of the most advanced software available to the federal government. 

There’s no visible damage to the drone in a photo included in the report, so von Stein said it’s unlikely the power failure was caused by a crash. In most other cases, he said, it’s operator error. 

While its manual warns to “remove the battery when it is turned on,” the Mavic 2 does have fail safes built in that allows the drone to store recordings in several places when its power is cut off by simply by putting in a battery again. 

Von Stein was able to easily recreate this in his lab, as CJI’s app was able to catch up once the battery was put back in. Baskerville’s report doesn’t state whether he tried putting a fresh battery into the Mavic 2, but one wasn’t mentioned in his report. 

Despite using several programs to pull data from the Mavic 2 Pro, Baskerville concluded in his report that the video files “contained no data and could not be reconstituted.”

‘We will bring it to light’

Monterrosa’s killing came amid a pandemic and the largest public outrage over police violence in modern U.S. history. The case received national attention as Monterrosa’s sisters, Michelle and Ashley, continued to push for justice for their brother. 

Asked about the possibility of evidence from the drone being destroyed, Ashley Monterrosa said “this is one of those cases where they shoot first and ask questions later.” 

“They want to get rid of whatever evidence that would signify there was no probable cause,” she said. 

Vallejo police Lt. Michael Nichelini, then-head of the department’s traffic division and president of its police union, was put on paid leave last July for allegedly destroying the windshield of the truck, which attorneys for Monterrosa’s family said was a key piece of evidence. Crime scene logs say Nichelini was at the Walgreens the morning of the shooting assisting with the investigation. 

Lt.  Fabio Rodriguez, head of investigations, was also put on leave around the same time. The state Justice Department opened an investigation into Vallejo police policies and the destruction of the windshield but declined at the time to review the Monterrosa shooting.

But the DOJ said it turned over its investigative file into the alleged destruction of evidence to the Solano County District Attorney’s Office four months ago when Xavier Becerra was attorney general. A DOJ spokesperson declined to elaborate on the findings.

Chief Williams sent Nichelini a notice of termination on Dec. 21, not long after a VPOA email was sent to then-San Francisco Chronicle columnist Otis Taylor Jr., who took the message as a threat. Weeks before he was fired, Nichelini filed a lawsuit seeking $7.5 million in damages from the department and city, claiming unjust treatment. Days after he was terminated, Nichelini filed an amended complaint seeking $10 million and his old job back.  

On May 13, Attorney General Rob Bonta, who Gov. Gavin Newsom appointed earlier this year, announced that his office would take over the investigation into Monterrosa’s shooting. In his announcement, Bonta said the police investigation was done by March 10. The findings were given to Solano County District Attorney Krishna Abrams’ office, which then tried to deliver the investigative file to the Justice Department, according to Bonta.

Abrams tried to do something similar with Becerra, regarding the file from the 2019 Vallejo police killing of Willie McCoy Jr. The DOJ refused to get involved, saying there was no reason local authorities couldn’t handle it. 

Abrams’ office did not respond to a request for comment. 

None of the agencies have publicly disclosed Vallejo police’s findings in those cases.

In August, when Bonta was a state assemblymember in the East Bay, he voted in favor of AB1506, which requires the state DOJ to conduct an independent investigation into any fatal police shooting involving an unarmed person. That law goes into effect in July.

Whether Monterrosa would be considered armed under the new law is unclear because he had a hammer in the pocket of his sweatshirt. But Bonta’s starting with that case.

Bonta instead said in a statement that he was stepping in because Abrams had abdicated her responsibility.

“Seeing the failure of the District Attorney to fulfill this important responsibility, my office will review the [Monterrosa] case to ensure a fair, thorough, and transparent process is completed,” Bonta said. “If there has been wrongdoing, we will bring it to light.”


Brian Krans is a freelance reporter in the East Bay who covers public health, from cops to COVID. Follow him on Twitter: @citizenkrans. Investigative reporter Scott Morris was editor for this article

Published by Brian Krans

Brian Krans is a freelance reporter in the East Bay who covers public health, from cops to COVID. Follow him on Twitter: @citizenkrans.

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