The family of Ezell Ford, an unarmed black man shot and killed on Monday night by Los Angeles police, will file a federal civil rights lawsuit against the LAPD, their lawyer says. During an interview with MSNBC’s “All In With Chris Hayes" Wednesday, attorney Steven Lerman said he will be filing the suit “immediately.”

"Justice will come to this family in federal court, not on TV," Lerman said.

Ford was the fourth unarmed black man killed by police in the country in recent weeks, Mother Jones magazine notes.

Ford was shot by a LAPD officer following what authorities describe as an “investigative stop” in the South L.A. neighborhood of Florence, an LAPD news release says. In its statement, the department says a “struggle ensued” during the stop and officers fired at the 25-year-old man. Ford, who had some form of mental illness, was taken to a hospital, where he later died from his injuries. No officers were hurt in the incident.

Lerman said the family doesn’t know the conditions under which the man was stopped, and his team is working to figure out what happened. He added that Ford wasn’t a gang member and called allegations that Ford argued with officers or provoked them in any way “complete nonsense.”

When asked by Hayes if Ford was armed when he was shot, Lerman said he wasn’t. "No, no, no, no. He was not armed," Lerman said.

He continued, "He was mentally challenged. This is not the person that's lurking behind a corner with a gun. He's not a gangbanger. Walking down a city street, a citizen of Los Angeles, walking down a city street unarmed at 8 on a Monday night."

In an interview with local station KTLA Tuesday evening, Ford’s mother, Tritobia Ford, said her son was complying with officers’ instructions and was on the ground when they fired at him. A second witness, who identified himself only as Ford’s cousin, told KTLA that officers were aware of the young man’s mental problems but shot him anyway.

“They laid him out and, for whatever reason, they shot him in the back, knowing mentally, he has complications. Every officer in this area, from the Newton Division, knows that — that this child has mental problems,” the witness said. “The excessive force … there was no purpose for it. The multiple shootings in the back while he’s laying down? No. Then when the mom comes, they don’t try to console her … they pull the billy clubs out.”

Lerman said the use of force was unnecessary. "I can't think of more innocent circumstances. But to be set upon by these officers who absolutely lost control and went to deadly force. This young man, what kind of fight could he have put up. Really, this is as sickening as it is said," he told Hayes.

The officer who shot Ford is currently on paid administrative leave, Sgt. Barry Montgomery said. The incident is being investigated by the LAPD and will be reviewed by the chief, the Office of the Inspector General and Board of Police Commissioners, the department said.