They also filled in some of the blanks about what happened before Prosa wound up driving the wrong way down Highway 427, leading to a head-on crash with another vehicle that killed a father and his teen daughter.
High school friend Tallyson Nebes told the court he was amazed when he learned of the Aug. 5, 2012 crash.
Nebes said he was "surprised that [Prosa] would do that, that he was capable of doing that."
Another friend, Francesco Turano, testified Prosa arrived at his house about 10:30 p.m.
Prosa had as many as six shots of vodka before Nebes drove them to a rooftop bar at The Guvernment around 11:30 p.m.
Nebes said Prosa was tipsy at Turano's home. By the time they arrived at the nightclub they were, "Joking, laughing, talking loud … the alcohol kicked in," Nebes said.
Turano said the three had at least three shots in about an hour before they lost track of Prosa at the club.
Turano and Nebes took a cab home without Prosa between 2:30 a.m. and 3 a.m — about the same time Prosa was driving the wrong way on Highway 427, where he crashed into an oncoming minivan.
The crash killed 49-year-old Neil Wijeratne and his 16-year-old daughter, Eleesha Wijeratne. Neil Wijeratne's wife, Antonette, was also seriously injured.
Prosa, 22, has said he doesn't remember much from the night, but testified on Wednesday he would never drive drunk. He has said he believes someone slipped something into his drink.
When asked by an arresting officer if he'd taken drugs or alcohol, Prosa answered "I drank a lot," according to an agreed-upon statement of facts.
A blood test found he had about twice the legal limit of alcohol in his system. But Prosa's lawyer, Alan Gold, wants the charges dropped because the blood sample was lost and cannot be independently tested.
Crown attorney Tom Goddard, while cross examining Prosa, remarked that when "facing hard truths — sometimes the less you remember, the better?"
"Some people might think that," Prosa replied.
The defence plans to call a toxicologist to discuss the effects of drugs on a body when the trial resumes next week.