Sentence set for Vic girlfriend killer

The odds that a man shot his girlfriend in the head without knowingly pointing the gun towards her are "astronomical", a Melbourne court has been told.

Nelson Lai, 35, insisted at his trial for murdering Rekiah O'Donnell, 22, in 2013 that he wasn't looking where the gun was pointed because he didn't think it was loaded.

He faced a plea hearing in Victorian Supreme Court on Tuesday after being found not guilty of murder but guilty of manslaughter by shooting his girlfriend in the head.

"The odds of it occurring by pure chance are astronomical," Crown prosecutor Andrew Grant said, as he and defence barrister Kevin Doyle presented their contrasting arguments about Lai's handling of the gun.

During his trial, the court heard Lai had been waving the gun around his bedroom on the morning of October 11.

Lai said Ms O'Donnell's death was a tragic accident and he would not have pulled the trigger if he had known the gun was loaded.

Mr Grant has argued Lai pointed the gun at Ms O'Donnell to intimidate her, but Mr Doyle on Tuesday accused the prosecution of speculation and said they were "gap filling" their case ahead of sentence.

He also disagreed with Mr Grant that the drug ice was an aggravating factor in Lai's case.

Lai's trial heard he had smoked ice about 2am the morning of the shooting.

But he denied he was angry, or in a rage because he was coming down off the drug.

He said he had been in bed, waving the borrowed gun around, pulling the trigger, when he heard a bang, then a thump.

Ms O'Donnell was shot through the head and died.

Justice Michael Croucher will sentence Lai on July 31.