Soham murder suspect Ian Huntley was admitted to hospital today after taking an overdose, sources said.
The Prison Service said a prisoner from HMP Woodhill, Buckinghamshire was taken to hospital earlier today.
Huntley, who is accused of the murder of Holly Wells and Jessica Chapman, was believed to be in a "life–threatening" condition.
A prison source confirmed that Huntley had been on suicide watch since his last court appearance in April. He is understood to have been receiving medication for depression for some time, the source said.
He was taken from the prison near Milton Keynes, Buckinghamshire, earlier today and was being treated in an outside hospital, officials said.
A Prison Service spokesman said: "A prisoner from HMP Woodhill has been admitted to hospital following a serious incident of self–harm."
A spokesman for Buckinghamshire Ambulance Service said an ambulance was called to the prison at about 3am and took a patient to Milton Keynes General Hospital.
A Prison Service spokesman later confirmed Huntley's identity and said he was taken to hospital at 4am.
Huntley and Carr both appeared at the Old Bailey in April in connection with the Soham case.
The parents of the two girls watched as Huntley, aged 29, who worked at Soham Village College at the time the girls disappeared, denied their murders.
Carr, aged 26, who was a teaching assistant in Holly and Jessica's class at St Andrew's Primary School, Soham, and lived with Huntley, denied two charges of assisting an offender and one of conspiring to pervert the course of justice.
Their Old Bailey trial is scheduled to begin on 6 October. Carr is being held at Holloway Prison, north London, while Huntley was remanded to Woodhill.
The two girls vanished on 4 August last year after being seen walking near their family homes in Soham. Their bodies were found on 17 August in a ditch near Lakenheath, Suffolk.
Carr also had to be taken to hospital from prison last year, when sources said she was treated for a long–standing eating disorder.
She was kept at Whittington Hospital in London for less than 24 hours. She was understood to have been receiving treatment for the problem since before her arrest in August.
Huntley was initially assessed at Rampton high security hospital in Nottinghamshire under the Mental Health Act, until psychiatrists said he was fit to stand trial.