Prosecutors say 49-year-old Johnnie Lee Wiggins killed his girlfriend, 55-year-old Prudence Hockley, outside of her Seattle home on Christmas Eve in 2011.
On the night of her murder, Hockley stepped outside at about 11 p.m. to talk with a friend, said Seattle Police Department spokesman Jeff Kappel.
Witnesses heard a loud thump, and Hockley's 13-year-old daughter went outside to find her mother unconscious, Kappel added. Neighbors report seeing a man walking away from Hockley and speeding off in his car.
Hockley also has an adult daughter, who told police that her mother had described Wiggins as controlling, jealous and short tempered, according to court documents.
Wiggins has a criminal history in Washington and North Carolina and he is a convicted felon in the state of Georgia.
He had been in Washington under supervised release from Georgia. That released ended when a community corrections officer said he found steroids at Wiggins' home.
Monday's verdict included the aggravating factor that the assault was committed in the presence of a minor child. During a short proceeding after the verdict, the jury found a second aggravating factor that Wiggins had an aggravated history of domestic violence with other victims.
Wiggins will be sentenced July 19. The standard sentence range is 20 to 30 years in prison, but the court can go above that range based on the two aggravating factors, according to prosecutors.