Johnnie Lee Wiggins, 49, 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.
At Friday's sentencing hearing, Wiggins apologized to Hockley's daughters for taking away their mother.
"I can't take it back. I can't make it go away," he said. "For the rest of my life I'll always want this to go away, but I won't be able to do it."
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.
In June, a jury convicted Wiggins of second degree murder, which included and aggravating factor that the assault was committed in the presence of a minor child, according to prosecutors.
The jury also found a second aggravating factor that the defendant had an aggravated history of domestic violence against other women.
Hockley's former husband, Leonard Smith, was also at the hearing, where he spoke directly to Wiggins.
"You've taken so many things, and so what we want to take from you now is we want to forget you," he said "We want to walk out of here today and forget your name, forget you existed, forget that you ever walked into our lives, forget that you ever went ahead and created the havoc that you've created, and then went forward as if nothing had ever happened."