Sean Monterrosa was a 22-year-old Latino American man who was fatally shot on June 2, 2020, by Vallejo police officer Jarrett Tonn. Monterrosa was on his knees and had his hands above his waist when Tonn shot him through the windshield of his unmarked police pickup truck. The police later said Tonn shot him because he erroneously believed a hammer in Monterrosa's pocket was a gun. Monterrosa later died at a local hospital.

The event sparked outrage in the Bay Area, particularly in Vallejo, which has a long history of police violence, excessive force complaints, and high-profile killings, including the February 2018 shooting of Ronnell Foster and the February 2019 shooting of Willie McCoy.

Sean Monterrosa (age 22) was of Argentinean and Salvadoran descent. He grew up in San Francisco and attended an arts high school. He had worked for a Boys & Girls Club and had recently been working as a carpenter. Less than an hour before Monterrosa was shot, he texted his sister a petition demanding justice for George Floyd, who was murdered by Minneapolis police a week earlier. Monterrosa was laid to rest on June 19, 2020. Jarrett Tonn has been a police officer in the Vallejo Police Department since 2014, after working for the Galt Police Department from 2007 to 2014. Monterrosa's killing was the fourth time in five years that Jarrett Tonn had shot at a person while on duty, including two shootings within six weeks in 2017 and a shooting in 2015 where Tonn fired 18 times. None of the three prior shootings resulted in a death and Tonn was cleared of wrongdoing by internal investigations in each case. Fifteen days after the fatal shooting of Monterrosa, Tonn was named in an unrelated excessive force and civil rights lawsuit in federal court.

Vallejo Police Department Over the prior decade, Vallejo police shot 32 people, 18 of whom were killed, in which time no officer was fired for their role in a shooting. As of May 2019, the department had the highest per capita rate of police shootings in Northern California. Vallejo police killed people at a per capita rate over four times as high as neighboring city Richmond, a city with a similar population and similar high crime rate.

Monterrosa was killed at 12:30 a.m. on June 2, while the city of Vallejo was under curfew in response to looting. Police did not reveal his death until a June 3 news conference. Police chief Shawny Williams said police were responding to a report of a possible looting at a branch of Walgreens and when officers arrived they saw 10 to 12 people in the parking lot. Two vehicles, a black sedan and a silver pickup truck, fled the area, resulting in a car chase where the black car rammed an officer's car and injured an officer.

Three detectives who were not involved in the chase arrived at the scene, in an unmarked pickup truck. Two detectives were in the front seat, and one was in the rear. As the truck arrived at the scene, the detective in the backseat mounted and aimed his rifle; the body camera he was wearing did not record sound in the seconds preceding the encounter. Just as the truck came to a stop, the detective in the back seat, later determined to be Jarrett Tonn, fired a rifle five times, through the windshield of the vehicle. One bullet struck Monterrosa in the back of the head. Immediately upon exiting the truck Tonn was recorded saying "What did he point at us?" The driver responded "I don't know man." Tonn then shouted "Hey, he pointed a gun at us!" At no point in the immediate aftermath of the incident was the shooting officer separated from other involved officers.

Tonn claimed Monterrosa appeared to be running towards the black sedan involved in the chase but he suddenly stopped, took a kneeling position, and placed his hands above his waist. No firearms were found with Monterrosa. The involved detectives claim that they mistook the end of a 15-inch hammer sticking out of his sweatshirt pocket for a gun.

In June 2020, U.S. Representative Mike Thompson and Assemblyperson Tim Grayson called for an independent investigation into the shooting, with Grayson saying that "it is absolutely unacceptable that the public was forced to wait for over 24 hours to learn of the conditions of those involved in the shooting," regardless of the circumstances.