Garrison has pleaded guilty to charges of vehicular manslaughter without gross negligence, driving under the influence and providing alcohol to a minor.
In December 2006, Vahagn Sedian was a passenger in Garrison's Land Rover when the actor lost control of the vehicle and crashed after leaving a pre-Christmas party. The 17-year-old was later pronounced dead in the hospital.
Garrison appeared at a Los Angeles County Superior Court in Beverly Hills on Thursday for sentencing, where the parents of Sedian took to the stand to give their accounts on how their son's death has impacted their family.
In his statement to the court, Sedian's father accused the actor of exaggerating his grief over the teen's death and criticized him for being "selfish."
He told the court, "He is an actor. He is acting. He killed a human being and he killed our son.
"Yesterday was one of the hardest days. It was Vahagn's birthday. He would have been 18. Nothing we say here today will bring Vahagn back.
"He's selfish. He took no responsibility. He could have come to us the next day and apologized, but he didn't."
Meanwhile, Michelle Ohana, who was also in the car with Garrison at the time of the crash, has blasted the 27-year-old for initially lying about who was behind the wheel, reports TMZ.com.
She told the court, "I was in shock when I heard Vahagn was driving. How could he lie to me when I was in the hospital?"
Garrison faces a maximum prison sentence of six years and eight months.
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