Murder accused tried CPR, father says

Nelson Lai held his former girlfriend's head saying "I didn't know there was one in it" moments after his father heard a gunshot and screams, a court has heard.

Lai, 35, has pleaded not guilty to murdering Rekiah O'Donnell, who was found with a fatal gunshot wound to her head in his Sunshine home in October 2013.

Dennis Lai told his son's Supreme Court trial in Melbourne on Monday he ran into Nelson's room after hearing a "pop" followed by screaming to find Nelson with Ms O'Donnell.

Speaking Mandarin and using an interpreter, Mr Lai said his son started performing CPR after calling for an ambulance.

"He was breathing into the girl's mouth while my wife was pushing on her chest," he said.

Mr Lai said his son told him in Hakka, the East Timorese language they spoke at home, "I didn't know there was one in it".

He told the court he saw a gun on Nelson's bed.

Nelson told him: "I picked it up somewhere, I just got it somewhere".

The court has previously heard Lai was abusive toward Ms O'Donnell and she was seeking counselling to understand why she kept going back.

The trial before Justice Michael Croucher will continue on Tuesday when Lai's mother and several police are expected to give evidence.