Brandon Willie Martin, 27. (Credit: Riverside County District Attorney's Office) CORONA, Calif. - A former Major League Baseball prospect was convicted Thursday of beating three people to death, including his disabled father, at their family home in Corona in 2015, prosecutors said.On Tuesday, Brandon Willie Martin, 27, was found guilty of the murders of his father, Michael Martin, 64; his uncle, Ricky Andersen, 58; and Barry Swanson, 62, an ADT alarm installer.After four hours over two days of deliberating, the jury found Martin guilty on all seven counts, including first-degree murder.