Pirone told the Los Angeles jury that Grant used profanity and called him the "n-word" shortly before he was killed. Pirone says he yelled the same profanity and racial slur right back in Grant's face.
As the key witness in former BART officer Johannes Mehserle's murder trial took the stand, Pirone said he had a big brother relationship with Mehserle and that he acted as a mentor for the rookie officer.
Pirone's behavior on the platform is at the center of the case. Prosecutors paint the picture of an aggressor who incited the chaos that night.
"Of course he instigated it, he carried an attitude and he pumped up the other officers up in the way he was acting," Grant's uncle Cephus Johnson said.
Pirone testified that he pulled his Taser out almost immediately after arriving on the platform for "intimidation...to get compliance."
Surveillance video from the Fruitvale station shows Pirone pointing his Taser at the BART window into a packed car as he searches for Grant on the train.
Within seconds of walking up to Grant and his friends, Pirone admits to using profanity in his commands.
Pirone said of Grant, "He continued to verbally curse and say, 'You guys aren't even real police." And that Grant specifically said, "Why are you f---ing with me? You aren't even real cops."
Other BART passengers who testified earlier in the trial said Pirone threw Grant's friends to the ground. Pirone said that did not happen.
"I specifically remember telling him, 'I asked you nicely,' before I grabbed him," Pirone said of the man he pulled off the train. "I gave him a nudge and pushed him."
Pirone also told the jury that Mehserle used a voice he had never before heard just seconds before he fired the fatal shot.
"He said, 'I can't get his hands. They're in his waistband. I'm going to Tase him. Get up,'" Pirone said.
Pirone said he got up and thought he would see Taser prongs in Grant's back. Instead he testified that the image of the bullet hole is one he will never forget.
Mesherle tried to talk to Pirone after the shooting.
"He said, 'I thought he was going for a gun.' I was like, 'Yeah, OK, man,'" Pirone said.
"He created that scene, he inspired and encouraged the other officers to perform as he did and that's why Oscar was murdered," Johnson said.