The family of a man killed by San Francisco police in the Mission District filed a federal civil rights lawsuit Friday, saying evidence and eyewitnesses contradicted the police explanation that officers had fired in self-defense to stop a robber with a knife.

The suit, filed by the parents of Guatemalan immigrant Amilcar Perez-Lopez, names the city, Police Chief Greg Suhr and the officers who shot the 21-year-old man. At a news conference Friday, the family’s attorney demanded that the chief recant his account of the shooting, that the investigation be taken over by federal authorities, and that the officers be criminally prosecuted.

The attorney, Arnoldo Casillas, said Perez-Lopez was not a robber and was running away from plainclothes officers who failed to identify themselves when he was shot in the back.

“Chief Suhr has been repeating the version of what the officers told him despite its falsity,” Casillas said. “The official version is a lie.”

Suhr and other police officials have said the fatal confrontation began around 9:45 p.m. on Feb. 26 on Folsom Street, just off the bustling 24th Street corridor, when police received a call about a man with a knife chasing a second man.

Perez-Lopez was attempting to steal a bike from the second man, officials said. They said that when two plainclothes officers responded and ordered Perez-Lopez to drop the knife, he charged at them with the knife raised overhead, forcing the officers to fire the fatal shots.

“The officers, as they are only allowed to fire in defense of themselves or others, felt that one of those situations was in play,” Suhr said the day after the shooting.

Police officials said both officers, Craig Tiffe and Eric Reboli, wore badges on the outside of their clothing.

The police explanation runs counter to what three eyewitnesses, including the alleged victim of the bicycle theft, told private investigators hired by the family, Casillas said Friday.

Casillas said the alleged bike-theft victim — whom he identified only as “Mr. Perez,” — told the investigators that he was in heated negotiations to sell a bicycle to Perez-Lopez, and that Perez-Lopez had threatened him with a knife, prompting someone to call 911.

Private autopsy

But according to the lawsuit, Perez-Lopez was already returning home when the officers arrived.

“One of the officers grabbed Amilcar Perez-Lopez and secured a bear-hug hold around Amilcar’s petite upper body,” the suit alleges. “Because Tiffe and Reboli wore civilian clothing, and did not identify themselves, Amilcar was not able to determine that the men were police officers. Amilcar broke free by wriggling out from the officer’s hold.”

Perez-Lopez had fled into the street between two parked cars when police opened fire, Casillas said. He was struck six times, according to a private autopsy done at the request of the family by Dr. Jay Chapman, a forensic pathologist with the Sonoma County coroner’s office.

Four shots hit Perez-Lopez in the back, one hit him in the back of the right arm and one hit him in the head, according to the private autopsy. The trajectory of the shot that hit him in the arm, Casillas said, showed the arm could not have been raised overhead.

The San Francisco medical examiner’s office has not yet released its autopsy report.

Eyewitnesses heard the sound of the metal knife hitting the pavement before the shots rang out, said Casillas, who did not identify these witnesses.

Suhr did not respond Friday to a request for comment on the lawsuit, but a police spokesman said the shooting “is still an open investigation” which is being conducted by the Police Department homicide detail, the Office of Citizen Complaints, the district attorney’s office and police internal affairs.

'Truly want justice’

Both Tiffe and Reboli have returned to active duty, police said.

At Friday’s news conference, Perez-Lopez’s parents spoke via Skype from Northern Guatemala where they live. In their native Spanish, Margarita Lopez and Juan Perez pleaded for justice for their son, who they said came to America to earn money, which he dutifully sent home.

“They truly want justice,” Casillas said. “The last thing they expected when they sent their son here was for him to come back the way he did.”

Casillas said he viewed Perez-Lopez’s death as emblematic of larger problems with the San Francisco police force, pointing to a recent scandal over several officers exchanging racist and homophobic text messages. He said he made a formal request to the U.S. Department of Justice to take over the investigation into the shooting.

Kale Williams is a San Francisco Chronicle staff writer. E-mail: kwilliams@sfchronicle.com Twitter: @sfkale