Tobby Carrier, who was 19 at the time of his older brother's death, is charged with first degree murder for the killing of Ismaël, 21, and with two counts of attempted murder.
He has pleaded not guilty to all charges.
Nelson Carrier, 57, told the 12 members of the jury he had just come upstairs when he heard his wife's piercing and muffled screams coming from the bathroom, on the day of the events in question, March 31, 2009,
He said he opened the door when she failed to answer and found her lying on the floor, inert.
Carrier said then he felt punches to his head and a burning sensation.
He said it took him several seconds to realize that his son Tobby was attacking him.
The father of the accused told the jury that he kicked his son to the floor and asked him, "What did we do to you?"
He said his son answered, "You brought me into this world."
Carrier said he went to find a baseball bat that he normally kept by his bedside table, but it was not there.
He then headed downstairs to look for it and saw the accused attack his other son, Ismaël.
Carrier told the court he witnessed Ismaël take his last breath as he lay on the floor.
Earlier this morning, the court heard from a former friend of the accused, Marie-Michèle Lévesque, who was 16 at the time of the attack.
Lévesque said she chatted with the 19-year-old over the internet before the incident.
She testified that he quickly began talking about death and had added a line to his chat handle that read, "The punisher. No doubt these are some of my last days here."
He then reassured her he was not talking about suicide but had "something in his hands" and he couldn't wait to use it.
She asked him repeatedly what the item was but he wouldn't respond.
According to Lévesque, the accused had spoken frequently about how much he disliked his parents, particularly his father.
On Monday, Crown prosecutor Guy Loiselle suggested that Tobby Carrier had been planning to kill his family members since he was 12 or 13.Suggest a correction