Fearing that his business partner, Romuald Ngande, 21, was about to attack him with a straight razor, Anthony Johnson fired one shot from an assault rifle, striking Ngande in the abdomen.
The two had been arguing over business matters in the early morning hours of Nov. 15, 2011, Johnson testified during his murder trial Monday.
He said he was in his bedroom in an apartment the two shared.
He said Nganda kept knocking on his door and urging him to come out and fight.
Fearing Ngande would open the door, Johnson said he grabbed an assault rifle lying on his bed.
"I put the clip in and chambered a round and went to the door and told him not to come in my room," Johnson testified.
He said Ngande managed to get the door open and as Ngande stood in the hallway, he said he saw him take a "shiny bling" out of his pocket.
He said he feared it was a straight razor Ngande was known to carry.
"I backed up and fired," Johnson said, a shot he insisted he fired in self-defense.
Closing arguments and jury deliberations are set for first thing Tuesday morning in Judge Melisa Skinner's 290th District Court.
If he is found guilty, Johnson is facing a maximum sentence of life in prison.