Michelle Carter encouraged her boyfriend to suicide. Now, his mother has spoken.

Hours on from their son’s former girlfriend being convicted of involuntary manslaughter, the parents of Conrad Roy III have spoken, saying Michelle Carter should be held responsible for not intervening in, and actively encouraging, their son’s suicide plan.

“I don’t believe she has a conscience,” Conrad’s mother, Lynn Roy told 48 Hours. “I think she needs to be held responsible for her actions ‘cause she knew exactly what she was doing and what she said.”

Having battled with anxiety and depression for a number of years, Roy III died in July 2014 after Carter sent him a barrage of text messages urging him to kill himself.

Filling his truck with toxic, Roy III, who was 18 at the time, hopped out and told his girlfriend via text message that he was scared.

"Get back in," Carter replied.

Carter, who was 17 at the time, is now facing up to 20 years in prison for failing to intervene and failing to alert either Roy's parents or authorities to what was happening.

"She did not issue a simple additional instruction: Get out of the truck," Judge Lawrence Moniz said this week.

According to the New York Times, Roy III's father Conrad Roy Jr said following the trial, “This has been a very tough time for our family and we’d like to process this verdict that we’re happy with”.

If you or a loved one is suffering with poor mental health, Mamamia urges you to contact Lifeline on 13 11 14, or BeyondBlue.