Pirone left his partner, Officer Marysol Domenici, who was handling a separate issue at a station agent's booth, and climbed the stairs to the station platform about 2:04 a.m. He stopped three black men who'd just walked off the train, telling them either to "sit the fuck down" or "get on the fucking wall," according to what they told investigators.

When Domenici joined him, he told her to "watch these guys," while he ordered Grant over to the wall.

Pirone then got on the train to detain a passenger named Michael Greer. Witnesses described Pirone as loud, aggressive and profane, with one saying the officer yelled, "Get the fuck out of my car" before dragging Greer off the train and handcuffing him.

Grant, meanwhile, was telling his friends against the wall to "just be cool" and "be quiet — we’re going to go home tonight" as they argued with Domenici, according to Jack Bryson Jr., one of the detained men.

Pirone told investigators he saw Grant fighting with Domenici and that he rushed to help her.

"The video, however, shows a completely different story, one of Grant pushing his friends back from Domenici and no touching of her ever taking place," the report says.

When he reached Grant, Pirone told investigators they scuffled. But the report notes that video of the incident shows Pirone shoved Grant against the wall and punched him in the head and that Grant did not fight back.

"Pirone accomplished his apparent intended goal to have Grant sit down. Once down, Pirone kneed Grant in the face," the report says, calling the strike "punitive" and unjustified.

Officer Used Racial Epithet

Pirone told investigators that Grant called him a "bitch-ass n-----" and that he responded by saying, "bitch-ass n-----, huh?"

"For a white law enforcement officer to utter the word 'n-----' to an African American male while detaining him in the tense racial atmosphere at the Fruitvale station undoubtedly contributed to the escalation of tensions," the report says. "The use of such a word diminished Officer Pirone and the BART PD."

At that point, the report says, Pirone and Mehserle began struggling to handcuff Grant.

Mehserle shoved Grant down, and Pirone put his knee on Grant's neck and head. The internal investigation found that Pirone's weight likely prevented Grant from getting his hands out from under his stomach to put them behind his back.

"When Pirone takes his weight off Grant, Grant immediately puts both hands behind his back for cuffing," the report says.

That's when Mehserle drew his gun and fired.

Nigel Bryson, one of the men detained along the wall, told investigators he heard the gunshot, then looked over to see Grant raise his head slightly and say, "You shot me."

The report found Pirone’s conduct played a major part in setting the stage for the shooting and recommended he be fired.

"Pirone’s repeated, unreasonable and unnecessary use of force; his willful and reckless conduct that endangered the safety of the public and his fellow officers; his failure to be forthcoming about the true events; his changing and shifting stories; his manifest lack of veracity; his professionally inappropriate demeanor; his use of a racially offensive word; and his excessive use of expletives, warrant a recommendation that Officer Pirone be terminated from his employment with BART,” investigators concluded.

BART subsequently fired Pirone, who was not criminally charged in connection with the Grant shooting. An arbitrator upheld that decision in 2014.

In the wake of the Grant case, BART implemented a series of steps to improve oversight of the police force, including creating an independent police auditor's office and a citizens review board.

BART also settled wrongful death lawsuits brought by Grant's mother and daughter, agreeing to pay each more than $1 million.