Marcello Fracassi was "likely" sleep driving when he hit city worker Geoff Gaston, according to an expert in sleep disorders.
Psychiatrist Dr. Colin Shapiro testified for the defence Thursday and said that Fracassi has "parasomnia," a disorder characterized by abnormal or unusual behaviour during sleep.
Fracassi has told court he would sleep walk, pee in strange places in his house and have arguments with his wife at night and then wake with no memory of the incidents.
Shapiro testified he conducted tests on Fracassi and concluded that stress, sleep deprivation and alcohol "created the storm" that led to the collision
Gaston, 41, was hit by Fracassi's pickup truck while painting road lines overnight in downtown Alliston on June 20, 2014.
Fracassi, 33, has pleaded not guilty to seven charges including impaired driving causing death and fleeing the scene.
The accused says he has no memory of hitting Gaston.
"All of the factors point to the possibility of the episode being a sleep driving event...This is the most likely explanation...
There's no question he has a diagnosis of parasomnia," testified Dr. Shapiro.
"The more bizarre the behaviour it is more likely they're not aware of what they're doing."
At one point Shapiro referenced the 1987 case of Ken Parks of Toronto who drove 23 km before murdering his mother-in-law and attempting to kill his father-in-law.
Parks was tried and acquitted through a sleepwalking defence.
The Crown challenged Shapiro about his findings which the doctor conceded were made without Fracassi disclosing his secret gin-drinking two to three nights a week.
Fracassi blew more than twice the legal limit of alcohol hours after the crash.
"This is really an alcohol induced blackout," charged Crown attorney Frank Faveri.
Shapiro said he now knows Fracassi lied about his alcohol consumption but the doctor stuck to his conclusions.
"Are any of those a game-changer? In my opinion it does not...These are messy, as is often the case in these types of cases."
The Crown suggested Fracassi might simply have fallen asleep behind the wheel and was not "sleep driving."
Faveri questioned how Fracassi could hit Gaston and a co-worker who were wearing reflective clothing and not stop, then swerve to avoid a transport truck that tried to block his path.
"In some circumstances people do recognize some of the features in front of them...I can't fully explain it," Shapiro said.
Shapiro pointed out that Fracassi didn't try to hide his damaged truck saying that suggests the accused wasn't cognizant of the events.
"Isn't it just equally consistent with Mr. Fracassi being really drunk and not hiding the truck?" Faveri asked.
"Yes he was drunk," replied the doctor.
"Isn't it just as likely an alcohol-induced blackout as sleep walking? What tips the balance is that he's an alcoholic. He needs to drink. He wants to drink," charged the Crown.
After a long pause, Shapiro replied.
"I don't think I'm in a position to answer that question. I don't have all the information that I need."
The Crown continued to try to chip away at the sleep driving defence.
"Would you agree with me that alcohol induced blackout is a possibility here?" asked the Crown.
"It is a theoretical possibility," replied Shapiro.
Another doctor will be called to testify Friday.