The vile past of Carl Williams' killer Matthew Charles Johnson

THE jury in the Matthew Johnson trial knew he was a criminal, but heard nothing of his frighteningly violent past.

THE jury in the Matthew Johnson trial knew he was a criminal, but heard nothing of his frighteningly violent past.

More than a decade before he bashed Williams to death, he'd committed a strikingly similar crime in the very same unit of Barwon Prison - and claimed self-defence that time too.

And recently he faced a murder charge after an 18-year-old was shot dead over $50 worth of cannabis. That time, the jury believed him and he was cleared.

In 1998, he was part of a group of inmates that attacked a fellow prisoner for "giving information'' to authorities - and used the same weapon he killed Williams with.

The victim of that beating, killer Greg Brazel, had been put into an Acacia unit exercise yard alone for his own safety.

But even prison walls were no match for Johnson and his cronies, who were set on attacking him.

Using a rowing machine and chair, the group pounded the armoured glass protecting Brazel for 45 minutes until they broke through, with Johnson then wielding a sandwich maker to inflict large gashes to his head.

A sandwich maker was something Johnson admitted to the jury he'd also considered using to kill Williams.

A prison officer reported seeing him use an exercise bike seat with the post attached to hit Brazel before punching and kicking him on the ground.

He ordered one of the others to stand guard and stop prison officers entering.

When charged over the assault, Johnson claimed Brazel had broken the glass himself and invited Johnson to enter before attacking him.

Johnson said he was forced to hit and kick him in self-defence.

During the County Court trial the group threw a bag of excrement into the jury box and Johnson broke wind into a microphone.

Later, Johnson menacingly called out to the juror that had been struck by the excrement - by name.

They were banished from their own hearing to watch proceedings from another room linked by video camera.

There his co-offenders bared their buttocks at the camera and the group disrupted the hearing with the Collingwood theme song.

Johnson was also involved in bashing another prisoner in 1995 after breaking into a protection unit.

By the time of the Brazel attack he had already racked up 132 convictions.

His shocking record includes taking part in the infamous Port Phillip Prison riot in 1998, armed robberies and break-ins.

He was accused of shooting dead a teenager in 2007 over a $50 drug purchase.

"Before the deceased could explain himself, Johnson pulled out a nine millimetre pistol and shot him in the chest,'' the jury was told in that trial, with a co-offender giving evidence that he saw Johnson pull the trigger.

He was found not guilty of the crime. Johnson also recently pleaded guilty over a carjacking, in which he held up a mother and two teenagers at gunpoint as they sat in a McDonald's car park.