The 22-year-old Matane man is accused of first-degree murder and two counts of attempted murder, in connection with the attacks in his family home on Mar. 31, 2009.
Dr. Marie-Frédérique Allard told the jury she met with Tobby Carrier three times over the course of several weeks between Dec. 2010 and Jan. 2011, while he was incarcerated.
Allard diagnosed Carrier with long-term depression and borderline personality disorder — a condition often brought on by childhood trauma.
Escaped into video games
Earlier in the court proceedings, jurors were played a video of a police interrogation, in which Carrier said he had been abused as a child.
Allard described Carrier as a fragile young man who escaped a life he hated by immersing himself in the world of video games.
The jury has heard that the night before the stabbings, Carrier had stayed up all night, playing video games.
Carrier also testified that he had spent the afternoon before the attacks smoking marijuana at a friend's house.
Allard said that this may have contributed to Carrier's deteriorating emotional state, but she does not believe that Carrier was still under the influence of marijuana at the time of the stabbings.
Allard suggested the man's fatigue, coupled with his depression and suicidal thoughts, built up to a major depressive episode.
No capacity to form intent, Allard says
She said Carrier's description of "feeling his body stab his family without being able to stop it" is consistent with a dissociative episode.
She said people in a dissociative state often have memory blanks, as Carrier described in Thursday's testimony.
Allard said in that state, Carrier did not have the capacity to form intent to stab his parents or to kill his brother.
After Carrier fled the house that night, he testified that he told his friends he had tried to kill his family on purpose, in order to prove that he was tough enough to do it.
Allard said at that point Carrier was still not able to think rationally.
The trial continues.