Soham murderer Ian Huntley has left hospital after being treated for a suspected overdose.
Huntley is serving a life sentence at HMP Wakefield
Huntley, 33, returned to HMP Wakefield, where he is serving a life sentence for the murders of 10-year-olds Holly Wells and Jessica Chapman in Cambridgeshire.
A Prison Service spokeswoman said an investigation was under way into events at the prison on Friday afternoon.
Huntley's condition was not thought to be life-threatening. It is the third time he has tried to take his own life.
It is understood he did not lose consciousness and presented himself to prison staff.
BBC correspondent Danny Savage said the news will be a huge embarrassment for the Prison Service, whose job it is to keep Huntley alive.
Huntley is normally held in the healthcare section of the high-security jail, which is not the same as segregation.
Editor of the Prisons Handbook, Mark Leech, said: "This is a dreadful story for the Prison Service and a huge embarrassment for them, particularly as Huntley is the highest possible security category.
"It is going to require some heads to be banged together to sort this out - they really must get to grips with it because this is not the first time, by any means, that Huntley has tried to take his own life.
"If necessary any medication should be given by injection."
The Prison Service spokeswoman said: "We can confirm that Ian Huntley is being treated in hospital for a suspected overdose.
"We will be investigating events surrounding this incident."
She was not prepared to disclose the hospital at which Huntley was receiving treatment.
'Risk of self-harm'
In September 2005, High Court judge Mr Justice Moses ruled that Huntley, originally from Grimsby, North East Lincolnshire, must serve at least 40 years in prison.
He said the killings did not meet the criteria for a "whole-life tariff", but the 40-year term offered "little or no hope" of his release.
Huntley first tried to kill himself in June 2003 after saving up 29 anti-depressant pills in a box of teabags while awaiting trial for the murder of the two schoolgirls.
An official report into the 2003 suicide attempt said Huntley presented an "ongoing significant risk of self-harm".
In September 2006 he spent a day in hospital after being found unconscious in his cell following an overdose.
That incident prompted an urgent review of how Huntley is supervised by the head of the Prison Service's Standards Audit Unit, Rob Kellett.
Huntley has also been subjected to attacks from fellow inmates.
In October last year he was reportedly held at knifepoint after being ambushed on his way back to his cell after a meal.