He waits to hear the key turning in the lock, but it never will again.

Instead, one year after Liam was killed by his best mate, all he can do is cry himself to sleep and wonder "what if".

Liam's death at 22 was a "despicable act of betrayal" for which he'll never find forgiveness or understanding, Mr Cahill said on Tuesday.

It happened on May 30 last year at the hands of Rian Farrell, a man who was supposed to be Liam's best friend.

The men, both apprentice plumbers, had grown up together, friends through primary and high school and into their working lives.

Farrell had booked a Docklands apartment in Melbourne to celebrate his girlfriend's birthday, inviting close friends including Liam.

They'd been having a good time until Liam and another friend got into a physical fight.

Liam punched the other friend and then refused to leave the party.

The punching victim left with a group, leaving behind Liam, Farrell and a group of four women.

The atmosphere had changed and Farrell confronted Liam about why he wasn't leaving.

Liam punched Farrell and Farrell punched back. A fight between the men broke out and they grappled, moving around the open plan kitchen and living area.

Farrell later told police that it went on and on because there was no other men to break it up.

At some point, Farrell pulled a knife from a block in the kitchen and stabbed it into Liam's chest.

The 20cm blade went deep into Liam's chest, piercing his heart and a lung.

One of the girls screamed "no" and another saw a spray of blood on the wall.

Liam turned and left the apartment. He collapsed in the hallway and died.

Farrell called two friends telling them what he'd done before going into the hallway where he screamed "no, wake up".

"Please don't die. It can't be true," he said.

He told police at the scene that Liam was his best mate and he wanted to know if he'd be alright.

"My life's f***ed. I'm going to jail. Please sir can I have a cigarette? This isn't happening," he said.

He said he had killed Liam but he hadn't meant it, before asking the officer how long he'd spend in jail for manslaughter.

Supreme Court Justice Jane Dixon will answer that question when she sentences Farrell, who pleaded guilty to manslaughter.

Farrell, now 23, was initially charged with murder. He has already spent a year in custody.

In a statement, Farrell's father Barry offered condolences to the Cahill family and said they would do anything to give them back their son.

Australian Associated Press