"To me this is flat out murder," said attorney John Burris.
Burris announced a federal civil rights lawsuit on behalf of Sean Monterrosa's family against the city of Vallejo and Officer Jarret Tonn.
On June 2 Vallejo police responded to reports of looting outside a Walgreens.
WATCH: Vallejo police release bodycam video from fatal shooting of Sean Monterrosa
WARNING: The video below is graphic.
According to Chief Shawny Williams, Monterrosa was crouching down in a half-kneeling position, moving his hands towards his waist area revealing what appeared to be the butt of a handgun. It turned out to be a hammer.
The body camera video does not show what Monterrosa was doing.
According to the lawsuit, Tonn is the officer who shot and killed Monterrosa from the backseat of an unmarked police vehicle.
RELATED: Vallejo police captain wasn't wearing body cam when officer fatally shot Sean Monterrosa
"It was almost like a wild, like an animal, he's looking through his window, he sees some movement and he's like a deer hunter he shoots the moving object," said Burris.
Burris said Tonn didn't know what if anything Monterrosa had on him.
On the body-worn camera video you can hear Tonn say, "What did he point at us?"
"I don't know man," responds another officer.
RELATED: Solano County DA recuses herself from reviewing Vallejo police shootings of Sean Monterrosa, Willie McCoy
"Hey, he pointed a gun at us," Tonn then says.
The lawsuit also alleges Tonn has a history of excessive force having been involved in three other officer-involved shooting within the past five years. Those shootings were not fatal.
"We're very, very disturbed by not only that he's still in the department, that he's still on the streets but engaged in this level of force," said Burris.
"It's hard, we lost our only brother," said Michelle Monterrosa.
"We need accountability, we need Shawny Williams to fire the officer involved Jarret Tonn," Monterrosa continued.
VIDEO: Family speaks out after Vallejo police mistake hammer for gun and shoot, kill 22-year-old
In an emailed statement to the I-TEAM, the Vallejo Police department writes, "Our hearts go out to the Monterrosa family during this difficult time. We respect their right to initiate legal action and we respect the judicial process to follow. We know this is a painful step for the Monterrosa family. It is our sincere hope that this process will guide the family and our community toward healing."
The Attorney General's Office is currently investigating the destruction of the windshield Tonn fired through.
Monterrosa's mother urged the AG to also investigate her son's death.
"This is the moment where AG Baccera steps up like a real man and takes on the case," said Nora Monterrosa.