MARTINEZ -- A 32-year-old man testified at his murder trial Monday that he shot and killed his cousin in Richmond last year in self-defense, after the victim reached for a shotgun during a heated argument.

The Contra Costa District Attorney's Office seeks a murder conviction against Oakland resident Jafari Sargent, who admits to fatally shooting 27-year-old Isaiah Thomas Jr. of Richmond at another cousin's house on Sept. 12, 2012.

"In my mind, I was scared for my life," Sargent said on the witness stand. "He put fear in my heart."

Sargent said Thomas and their younger cousin Jarrell Boughton got together that night to check on their grandfather after the 84-year-old Richmond man was arrested on suspicion of shooting at another man. At least two of the men, Boughton and Sargent, were armed.

It was on their way back to Boughton's residence, Sargent said, that Boughton fired a shotgun out the car window in response to Thomas harassing him about being too cowardly to use his weapon.

The argument continued at Boughton's, and Thomas became "angrier and angrier" when Sargent said he wanted to go home. He couldn't leave, however, because Thomas' car was blocking his and Thomas refused to move the car or hand over his keys.

A fourth cousin, Mocha Boughton, tried to intervene and get the car keys, but Thomas slapped his hands away and the two men began to struggle, according to Sargent. Mocha Boughton had fallen down when Thomas jumped on to a bed and reached for Jarrell Boughton's shotgun.

Sargent said he was standing by the front door when he quickly shot his cousin once in the chest with his Glock pistol and then fled in a panic.

He said he loved his cousin, and never intended to shoot him or anyone else that night.

"Then why did you bring 24 bullets with you?" prosecutor Simon OConnell asked.

"I don't know," Sargent replied.

Attorneys are expected to give closing arguments in the case on Tuesday.

Contact Malaika Fraley at 925-234-1684. Follow her at Twitter.com/malaikafraley.