But Tate-Brown refused to be handcuffed and began fighting the officers, a struggle that raged for several minutes, Williams said. Tate-Brown broke free of police three times, finally lunging into his car's open passenger-side door to reach for the gun, Williams said.
That's when one officer shot him in the back of the head.
While Tate-Brown's irate family suggested the gun had been planted by corrupt police trying to cover up an unjustified shooting, DNA tests confirmed Tate-Brown had handled the semi-automatic Taurus handgun, which was fully loaded and had been reported stolen out of South Carolina in July 2013, Williams said.
"The facts show a tragedy, a terrible tragedy, but . . . the officers' actions here do not constitute a crime," Williams said. "This was not the case of an unarmed man shot while running away. It's a case of a struggle and of Mr. Brandon Tate-Brown's attempt to get his illegal gun."
Williams added: "The law allows an officer to use deadly force if he believes deadly force will be used against himself or others."
Police already had cleared both officers, whose names they have refused to release, of any departmental violations. Both are back on the street.
Williams said he met with Tanya Brown-Dickerson, Tate-Brown's mother yesterday morning and presented an overview of case evidence to about 20 religious and community leaders earlier this week.
Brown-Dickerson and her supporters have rallied weekly, calling on police to release the officers' names and video of the incident. They've created hashtags like #PPDSerialKillers and #JusticeforBrandon and circulated fliers showing Philly officers as wolves in police uniforms.
"Seth Williams said this is a tragedy, and I agree with that," Brown-Dickerson said during an afternoon news conference on a windswept corner of Dilworth Park, in the shadow of City Hall.
She spoke of video footage that she, her husband and their attorney, Brian Mildenberg, viewed at Internal Affairs headquarters.
"How is it our six eyes can see my son fall down, facedown, not on the right side of the car, and not reaching into the car, and they can't see that is beyond me."
Brown-Dickerson said she wants the video footage that she reviewed to be made public.
"I want you all to see what we three saw . . . and let the public and you make a decision."
Greg Brinkley, a private investigator working for Mildenberg's law firm, called the city's handling of the incident a "cover-up."
Williams showed one video of the incident to reporters during a midday news conference yesterday, but said he will not publicly release it because "we're not like the public library." It was tough to tell what was happening on it anyway, because a street sign, utility pole and flashing police lights largely obscured the camera's view.
"This is not a Hollywood production; we have no CGI. (Regarding evidence,) we have what we have," Williams said, admitting the flaw of such footage.
Williams acknowledged that his decision might not quell critics' concerns.
"Some people will be upset. There are some people who make a career out of being upset," Williams said.
"I am not here to demonize Mr. Brandon Tate-Brown," he added. "But neither am I here to demonize the police officers, who are trying to do a difficult and extremely dangerous job."
Mildenberg and Dickerson-Brown said they both support the police department, but want answers to a litany of questions that they feel haven't been adequately addressed, from the reason Tate-Brown was stopped by police to the names and histories of the officers involved in the shooting.
Mildenberg said he is continuing to explore filing a lawsuit over civil-rights issues, and noted that more information could come to light once he's able to file subpoenas and arrange depositions.
"There are substantial open questions and issues in this case," he said.
On Twitter: @DanaDiFilippo