An investigation has been launched after a 21-year-old prisoner – believed to be on suicide watch – died in his cell.

Billy Spiller, who lived with his family in Fishergate Close, Fishergate, near Portslade, was found dead at Aylesbury Young Offenders’ Institute (YOI) in Buckinghamshire.

Spiller, who had autism, was found hanging in his cell at the YOI on Saturday, just weeks after it was criticised in a damning report.

The report said the YOI, which mainly houses prisoners aged between 18 and 21 who have committed serious offences, had “no clear policy for safeguarding vulnerable prisoners”.

It added that prisoners were given “far too little to do” and were not encouraged to keep clean.

The Prison and Probation Ombudsman has now launched an investigation into Spiller’s death.

Yesterday a spokeswoman from the ombudsman said: “We can confirm that an investigation has been opened into the death of Billy Joe Spiller.

“This will run alongside the coroner’s inquest and any police investigation.

“Our report will be published after the inquest.”

The Buckinghamshire coroner confirmed an inquest had been opened and adjourned into Spiller’s death.

The Prison Service said Spiller, who was jailed for 42 months for attempted rape, sexual assault and one of exposure on December 3, 2009, was recalled to prison after breaching the terms of his licence.

He initially appeared at Worthing Magistrates’ Court and was convicted at Chichester Crown Court.

It was initially reported that Spiller was on suicide watch in the YOI but yesterday his father said he was not certain this was this case.

His father, who said he was too upset to talk, added he had visited Aylesbury since the incident. He said his son should never have been allowed to die in the way he did.

In a notice in The Argus his family paid tribute to Spiller, whose funeral will take place on Wednesday, November 16 at 11.30am in St Leonard’s Church, New Church Road, Hove.

They said: “You made us laugh, you made us cry, How can we ever say goodbye?

“Sometime from now, we don’t know when, We will all be together again.

“Love you loads mate.”