Louis Sweeney was the head of the Sweeney family who father a son, Carter Sweeney, and a daughter, Caitlin Sweeney. He is a convicted serial bomber known as the Sunnyview bomber who terrorized the LA area.
The LAPD started trying to build a case against Louis and with the help of Mark Sloan he was convicted of the bombings. He was executed for his crimes in "Obsession" which is when his son and daughter restarted the bombing campaign.