In the year since her son was killed, Tanya Brown-Dickerson has pored through the circumstances of his death in excruciating detail.

She has gone over the witness statements. Read and reread the Internal Affairs interview with the Philadelphia police officer who shot him. Monitored the news reports. Listened to explanations from the Police Department and the district attorney.

And she has seen the grainy surveillance footage that captured the car stop, the struggle, and the shot that ended Brandon Tate-Brown's life early on Dec. 15, 2014.

Sometimes she wishes she hadn't.

A year ago Tuesday, Tate-Brown was pulled over in his rental car on Frankford Avenue around 3 a.m. The officers who stopped the 26-year-old said they noticed a gun wedged in the front seat of the car, and ordered him out.

There was a scuffle. Tate-Brown broke away from the officers, several times. The officers said they believed he was trying to get the gun.

One officer shot him in the back of the head as he rounded the back of his car.

Brown-Dickerson has spent the last year fighting for information in her son's death - pleading with the city to release the name of the officer who killed him, the stories of the witnesses who saw him die, the video of his last moments.

She got them, thanks in part to a lawsuit still pending in federal court.

And now she dwells on the details, particularly Officer Nicholas Carelli's explanation to Internal Affairs on why he drew his gun on her son:

"I wanted to discharge before I lost sight of him because I feared that he would be able to get the gun before I would be able to protect myself."

To Brown-Dickerson, that means Carelli had a moment to weigh what he was about to do, and then still killed her son. She can't shake the thought.

"They say it'll get better, but it feels like yesterday," she said at her Frankford home last week. "The pain is still the same."

The choices of a parent whose child is killed by the police are few. You can protest to the point of exhaustion, yell until your voice gives out, search for answers that may never come. Or you can grapple with what is often the unspoken public narrative in these cases: A police officer was forced to protect himself, and so your child had to die.

Brown-Dickerson took to the streets the day her son was killed.

A supervisor at a school bus company, she had watched nationwide protests over the police-involved killings of black men in late 2014 and considered getting involved.

Once her oldest son was killed, Brown-Dickerson was thrust into a world of activism that sometimes gives her strength and sometimes overwhelms her.

"Two months ago, I said I need a break," she said. "I wonder - did you grieve Brandon the way you were supposed to? But I can't stop even if I wanted to now."

When Brown-Dickerson's son was killed, activists in Philadelphia flocked to the cause. The local branches of the NAACP and the National Action Network, and a group of clergy activists called POWER, lent their voices to the protests.

But Brandon Tate-Brown never became a household name. His case never grew as big or as studied as those of Michael Brown, or Eric Garner, or Freddie Gray.

"Brandon's story wasn't as big as everybody else's," Brown-Dickerson said last week with some sadness.

But his death triggered significant changes in how the city responds to police shootings.

The Police Department now releases the names of officers involved in shootings shortly after the incidents.

In Tate-Brown's case, the city ended up releasing an unprecedented set of documents connected to the investigation.

And although he said he arrived at the decision independently of the Tate-Brown case, Police Commissioner Charles H. Ramsey began to speak, often, of bringing in an outside agency to investigate police shootings.

At the time of Tate-Brown's death, the Police Department's approach to shootings was more circumspect. The only official initial response was a few paragraphs on its website.

For months, Brown-Dickerson and her supporters demanded the names of the officers involved, surveillance footage, statements from witnesses, anything that might shed more light on what had happened on the 6600 block of Frankford Avenue.

The details came slowly - first, grainy surveillance video of the shooting that Brown-Dickerson and her attorney were allowed to view in private.

In February, the officers involved in the case returned to street duty.

In March, District Attorney Seth Williams announced that the officers would not be charged in Tate-Brown's death, and provided the first detailed account of the shooting. Witnesses, he said, told investigators that Tate-Brown had appeared to be reaching into the car, ostensibly for the gun, when he was shot.

And, Williams said, Tate-Brown's DNA had been found on the weapon, a .22-caliber semiautomatic later found to have been reported stolen in South Carolina in 2013.

Brown-Dickerson's attorney has contended that news footage shows that the gun was mishandled at the scene, placed on the hood of a car covered in Tate-Brown's DNA.

"A court would not allow that gun to be presented as evidence," he said.

Said Brown-Dickerson: "I don't know why my son would have [a gun], let alone believe he did."

Then in June, the city released a cache of documents - detailed information of a sort that has not been made public in a police shooting before or since: witness statements in full, videos, and interviews with the officers who stopped Tate-Brown that night in Mayfair.

The account laid out in the documents differed in part from the department's original version of the shooting, which held that Tate-Brown had been shot while reaching into the passenger seat.

In the documents released in June, Carelli said he had shot Tate-Brown at the back of the car, to prevent him from getting to the gun.

Carelli could not be reached for comment. Fraternal Order of Police Lodge 5 president John McNesby did not return a call for comment.

Ramsey has said he can't comment extensively on the case because of the lawsuit.

But he said his department has worked for years to become more transparent on police shootings. He has suggested that an outside entity investigate police-involved shootings. and this year began releasing the names of officers involved in shootings within 72 hours of the incident, as long as no threats are leveled against the officers.

(The FOP is backing a bill in the state House that would bar municipalities from releasing the names of officers involved in shootings.)

Ramsey called Brown-Dickerson this year to express sympathy for her loss.

"Any time there's any loss of life, under any circumstances, it's something we take very seriously, to make sure that all policies and procedures were followed," Ramsey said.

After June's release of the documents in Tate-Brown's case, some saw it as a laudable step toward transparency in such cases. However, the city has not publicly released a comparable set of documents in the handful of police shootings since.

Brandon Tate-Brown's death was complicated. Brown-Dickerson's grief is simpler: that of a mother who has lost her son.

She spoke last week of a young man who loved his family, who grew up in a tough neighborhood and learned to defend himself and those he cared about. Who went to prison at 19 for shooting two men in a feud. Who was afraid of going back to jail.

He wrote poetry and developed a booming laugh, and told friends he was a "mama's boy."

He worked hard to turn his life around, she said, and was employed at Hertz when he was killed. The white Dodge Charger he was stopped in belonged to the company.

In September, Brown-Dickerson said, she passed a pair of officers on Frankford Avenue. They had pulled over a black man in a "big old beautiful Lincoln," she said. She stopped to take a look.

She saw one officer's name tag: Heng Dang, the other man who stopped her son. She saw the other officer's face. Figured it must be Carelli.

She wanted to cry, but she didn't want them to see. She thought of her son, of the long months waiting for answers, of that grainy video of his death.

"I said to myself, 'You're not doing this today to nobody else's child,' " she said.

Then she pulled out her cellphone, and started to record.

215-854-2961@aubreyjwhelan