Stephen Robinson admits he fatally stabbed his neighbour during a scuffle inside a Melbourne rooming house.
He believed Adam Russell, 49, who lived in the room next door, was trying to steal his bicycle to sell it for methamphetamine.
However, Robinson's lawyer has told a Supreme Court jury he is not a murderer. He was acting in self-defence.
"He doesn't deny the stabbing. He says he was being attacked by an ice addict, Mr Russell, and under attack he grabbed anything he could to defend himself," defence lawyer Amy Brennan said on Tuesday.
Robinson, 57, has pleaded not guilty to the August 2021 murder. A jury of five men and nine women were empanelled on the first day of his trial.
Prosecutor Mark Rochford KC said the two men lived in neighbouring rooms at Mossgiel Park Accommodation Homes in Endeavour Hills.
After 1.35pm on August 15, Robinson got ready for a bike ride and placed his bicycle outside his room. He leant it up against a lounge chair, partially blocking access to Mr Russell's room.
He went back into his room as he forgot his sunglasses, when Mr Russell, who was agitated and yelling at another neighbour, walked to his room and grabbed the bike.
Mr Rochford alleged he moved the bike to get it out of the way. The pair began arguing after Robinson grabbed the bike back from him.
The confrontation became physical, with punches thrown, and Robinson went to his room and retrieved a knife. Robinson then stabbed Mr Russell in the chest.
Mr Russell stumbled into the hallway and collapsed to the floor.
"He committed the act that caused the death. He did this, he stabbed him, with intention to kill," Mr Rochford said.
Following the scuffle, Robinson walked passed Mr Russell's body and went to the caretaker's room.
"Ring the police, I've stabbed Adam, I think he's dead," he told them.
He later told police, when he came out of the room he saw Mr Russell trying to steal his bike and "sell it for ice".
"I grabbed anything I could to defend myself and that's what I did, is there anything wrong with that?" he told police during his interview.
The trial before Justice Elizabeth Hollingworth continues.
