KNOXVILLE, Tenn. – A Knoxville Police Department arrest warrant provided more details about what took place in the hours after an 18-year-old woman was killed. The police department said authorities began a homicide investigation Monday, July 22, after responding to a report that 20-year-old Juan Carlos Diaz-Perez had gravely injured his girlfriend at a home on Mercer Street in North Knoxville.