Twenty-eight-year-old Matthew Foerster has admitted to attacking the woman in Armstrong, B.C., on Halloween night in 2011 but pleaded not guilty to first-degree murder.
B.C. Supreme Court Justice Peter Rogers has told a jury in Kelowna that a conviction of first-degree murder means the killing has to be planned and deliberate.
However, he says someone can still be found guilty of first-degree murder if a death is caused during a sexual assault or an attempted sexual assault.
The defence is calling for a verdict of manslaughter, saying Foerster was seeking consensual sex but that when Van Diest fought back, he pushed her down and caused her to fall and hit her head on a steel pipe.
But the Crown has said Foerster hit the teen on the head six times with a flashlight and tied a shoelace around her neck. (CKIZ)