Attorneys Billy Murphy and Jason Downs, right, hold a news conference with family members of Terrence Sterling, the Maryland motorcyclist who was fatally shot by a D.C. police officer on Sept. 11. (Nikki Kahn/The Washington Post)

An attorney for the family of a man fatally shot by D.C. police alleged Thursday that Terrence Sterling was killed “unlawfully and unjustifiably” and said his family wants more details about the incident.

Jason Downs, the attorney, criticized city officials for not releasing additional information about the circumstances surrounding the death of the 31-year-old motorcyclist, who police said was shot when he intentionally struck a police cruiser’s door as an officer was trying to get out.

Downs said the family wants to know how many times Sterling was shot, whether there are any surveillance videos that captured the shooting and whether the officer was inside his police car when he fired his gun.

Downs also noted that video viewed by Sterling’s family shows a union representative arriving at the scene before paramedics did. Downs said the family wants to know how quickly emergency medical help was summoned and why the union representative apparently arrived first. A union official said representatives who were on duty would have heard the radio call.

During the news conference, Downs and attorney William “Billy” Murphy Jr. said the Sterling family is grateful to those who have held demonstrations in the city and asked that those remain peaceful. Sterling’s family members stood with the attorneys, but his parents, sister and aunt declined to comment.

An attorney for the family of Terrence Sterling, who was fatally shot by D.C. police Sept. 11, criticized local officials on Sept. 29 for not releasing more information about the event. (WUSA)

Sterling, who had been an HVAC technician for a dozen years, was shot early the morning of Sept. 11 after police spotted a motorcyclist driving erratically, officials said.

Early this week, D.C. Mayor Muriel E. Bowser (D) released police body-camera footage of the aftermath of the shooting. In a departure from police policy, she also publicly identified the officer who fired his weapon as Brian Trainer, who has been on the force for four years.

Bowser said Thursday that, other than the body-camera footage, she was “not aware of any other video.” The mayor’s office has said it is seeking to be open about the case without jeopardizing the investigation.

“We understand this is a very sensitive matter,” said LaToya Foster, a spokeswoman for Bow­ser. “The mayor is always committed to transparency and accountability.”

The scrutiny comes as other cities across the country, including Charlotte and Tulsa, have also been reeling after fatal shootings by police.

Attorneys for Sterling’s family praised the mayor for releasing the video and identifying the officer. But they insisted that city officials are withholding too many details.

“We think there is a coverup,” Murphy said. His firm also represented the family of Freddie Gray, the Baltimore man who died last year after being injured in police custody.

On Sept.27, D.C. police released body camera footage showing the aftermath of the Sept. 11 fatal shooting of Terrence Sterling. Here's what they say led up to the shooting, and what happened after. (Claritza Jimenez/The Washington Post)

The attorneys alleged that Trainer and his partner, who has not been publicly named, may have violated multiple D.C. police regulations. The attorneys questioned whether the police cruiser was improperly used as a barricade and whether Trainer may have improperly fired at a moving vehicle or improperly fired from within a cruiser.

Sterling’s death, the attorneys said, was all too familiar.

“You have another innocent, unarmed black man killed by a police officer not only in D.C. and Baltimore, but across this country,” Downs said. Trainer is white, the attorneys said.

On Tuesday, the mayor’s office showed the Sterling family video from the body camera Trainer was wearing. They then released most of the footage to the public but said that for privacy reasons, they stopped it at the point when paramedics arrived.

The publicly released video, which lasts about five minutes, does not show the shooting because Trainer did not activate his body camera until one to three minutes after he shot Sterling, city officials said. The footage shows Sterling lying in the street as an officer performs CPR.

Downs said the full body-camera video later shows the arrival of an officer who identifies herself as a union representative. He said the representative tells Trainer to turn off his body camera after he tells her it is activated.

Sgt. Matthew Mahl, chairman of the D.C. police union, said at least two union officials were on duty as officers in the area that night and would have responded to a “critical incident.” He said the response would have been first as a police officer until the scene was secured and medical aid was being given to the shooting victim. After that, a union official would advise the officer.

D.C. police have referred questions to the mayor’s office.

The incident began about 4:20 a.m. when an officer spotted a motorcycle going erratically in the Adams Morgan area. On Thursday, Bowser’s office said Trainer and his partner first spotted a motorcycle at 15th and U streets Northwest.

Later, police saw a motorcycle near Third and M streets in Northwest, near the Third Street Tunnel, which is where the shooting occurred.

Officials said Trainer was trying to get out of the passenger’s side of a marked cruiser to stop Sterling. But at that point, according to police, Sterling drove the motorcycle into the passenger door and Trainer shot him.

Downs said the family thinks that Sterling was headed to his home in Fort Washington, Md.

The Chief Medical Examiner’s Office in the District said Sterling had two bullet wounds, one in his neck and another in his back. They did not say how many times he was shot.

Trainer and his partner, who was driving the police car, have been placed on paid administrative leave, which is standard in such cases. The investigation is being handled by a unit within the U.S. attorney’s office.

After Sterling’s shooting, police updated the department’s policy on body cameras, and officers are now required to confirm with dispatchers that their cameras are on when they respond to calls.

Aaron C. Davis and Clarence Williams contributed to this report.