He took the witness stand in the trial of Hosea Thomas, 34, who is accused of firing the shot that killed Philant Johnson during a gun battle on Interstate 75.
"All of those rounds were fired for me, in my opinion," he said, adding that he later apologized to Johnson's mother when he called her with the news.
Testifying for the prosecution, T.I. described seeing Johnson, whom he called his best and oldest friend, after their van pulled over. He said Johnson was lying lifeless, blood running down his face from a shot into his left temple.
Johnson was an assistant to T.I., whose real name is Clifford Harris.
T.I. said he and Johnson grew up together in Atlanta.
The shooting occurred after a post-concert party at a club. T.I. said after his van drove away, he spotted another vehicle moving up from behind in traffic. Then shots rang out and he took cover.
Three others were injured. T.I. wasn't hurt.
He testified that after calling Johnson's mother, he talked to Johnson's young daughter, whom he said was 4 or 5 years old.
"I told her that he was gone to a better place and he won't be coming back. And I told her how much he loved her," he said.
T.I. spoke calmly and directly during 30 minutes on the stand in a packed, small courtroom in the Hamilton County courthouse.
Prosecutors say Thomas' brother has identified him as the shooter. Padron Thomas was driving a Jeep that allegedly chased the vans used by T.I. and his entourage on May 3, 2006.
Hosea Thomas' attorney said Padron Thomas is testifying against his brother to earn a lesser sentence on federal charges.
T.I. has had his own legal problems. He was sentenced to one year in prison on federal weapons charges after his arrest in October 2007 before the BET Hip-Hop Awards in Atlanta for allegedly trying to buy automatic weapons. He is to start his sentence in March after completing 1,000 hours of community service.
His latest CD, "Paper Trail," debuted at No. 1 on the Billboard Top 200 album charts, and has produced two No. 1 singles, "Whatever You Like" and "Live Your Life" featuring Rihanna.