Carl WilliamsHomicide squad detectives have driven to Barwon Prison to take control of the investigation into the death of notorious underworld identity Carl Williams.

Williams, 39, died after he was attacked by fellow inmates in the prison early this afternoon.

An autopsy will be conducted to see if he died as a direct result of the attack or due to a heart attack.

Williams had been on a modified diet and had lost weight since he was sentenced to a minimum of 33 years in 2007 over four murders.

Detectives will investigate whether the attack was sparked by reports today that police had paid Williams’ daughter’s school fees.

Two plain-clothes police arrived at the home of Williams’ father, George, in Broadmeadows about 3.10pm.

The men, believed to be homicide squad detectives, were let into the property by an unknown man.

A friend of George Williams asked a reporter who knocked on the door to leave him alone.

A police spokeswoman confirmed there had been a death as a result of an assault at Barwon Prison.

Shortly after the news broke this afternoon, underworld figure Mick Gatto said he had heard rumours about Williams having died but said that was all he had heard.

‘‘I would rather let dead dogs lie,’’ he said.

‘‘If you hear any more let me know but I would rather not comment on him.’’

He said Williams was ‘‘certainly not’’ a friend.

Williams gained notoriety for his role in Melbourne’s gangland war.

He had one daughter, with former wife Roberta Williams.

In 2007, he pleaded guilty to murdering Jason Moran in June 2000, Lewis Moran in March 2004 and Mark Mallia in August 2003 and conspiracy to murder Mario Condello in May-June 2004.

He had previously been found guilty of the murder of Michael Marshall, killed in October 2003.

Williams was denied permission to attend the funeral of his beloved mother, Barbara, at the end of 2008 after he was deemed too much of a flight risk.

His father George was released from Barwon Prison in June last year after serving 20 months for drug trafficking.

with Robyn Grace, Reid Sexton, AAP