OAKLAND PARK, Fla. — The witnesses who saw a Broward County deputy sheriff kill a man who had strolled through his apartment complex with an unloaded air rifle propped on his shoulders agreed: Just before he was gunned down, Jermaine McBean had ignored the officers who stood behind him shouting for him to drop his weapon.

Nothing, the officer swore under oath, prevented Mr. McBean from hearing the screaming officers.

Newly obtained photographic evidence in the July 2013 shooting of Mr. McBean, a 33-year-old computer-networking engineer, shows that contrary to repeated assertions by the Broward Sheriff’s Office, he was wearing earbuds when he was shot, suggesting that he was listening to music and did not hear the officers. The earphones somehow wound up in the dead man’s pocket, records show.

“I want justice for something that went totally wrong.” Mr. McBean’s mother, Jennifer Young, said in an interview. She added that she believed officers had profiled her son because he was black.

A federal wrongful death lawsuit filed May 11 accused the Broward Sheriff’s Office of tampering with evidence and obstructing justice. The suit alleges that the deputy who shot Mr. McBean perjured himself and that the department covered it up by giving him a bravery award shortly after the killing, while the shooting was still under investigation.