Willie Clinton Mack

Willie Clinton Mack sits in court following jury selection in his trial for second-degree murder May 5.

Testimony began Wednesday in the second-degree murder trial of Willie Clinton Mack, who is accusing of stabbing his sister's boyfriend to death. 

On Feb. 5, 2016, Mack had gone to a party to celebrate his birthday along with his sister; her boyfriend, Derick Ulysses Alston; and her teenage daughter.