Shawndel Weems, 23, of Columbia, was found guilty of fatally shooting Simeon Mbuyu Mukuna, an 18-year-old student at Richard Montgomery High School, in February.
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According to police, Mukuna was helping a friend fix their car at an apartment complex on Monarch Mills Way Saturday evening.
Witnesses say Mukuna went to get a jacket out of his car. As he walked back across the parking lot, Weems pulled up beside him and fired nearly a dozen shots, killing the teen.
Charging documents say Weems told police he felt Mukuna, the victim, was going to try to harm him.
He also told police he had never seen Mukuna before.