School caretaker Mr Ian Huntley has been charged with the murder of schoolgirls Holly Wells and Jessica Chapman. Mr Huntley has also been sectioned under the Mental Health Act of 1983.
He was transferred at 2 a.m. from his police cell to Rampton hospital in Nottinghamshire on the advice of a psychiatrist concerned at his fitness to be interviewed over the murder of the girls.
The girls' parents were informed in advance of the decision to charge Mr Huntley.
They are still waiting to hear how their daughters died after a postmortem examination proved inconclusive.
The bodies of the best friends were found by walkers at a Suffolk beauty spot on Saturday, almost two weeks after they vanished from Soham wearing identical Manchester United football shirts.
Mr Huntley was charged at about 5 p.m. by two Cambridgeshire detectives who drove to Rampton.
Doctors must decide if he is physically fit to attend the court. Psychiatrists have up to 28 days to assess Mr Huntley but can apply for further extensions up to six months or more.
A spokesman for Rampton hospital said its patient would remain "for an undetermined stay".
It is still possible that a patient deemed to need mental health care could stand trial for murder, a Cambridgeshire police spokesman said.
The decision to charge Mr Huntley followed "lengthy discussions" with the Crown Prosecution Service, Detective Chief Inspector Andy Hebb said at a news conference in Huntingdon.
Police are still searching the site where the bodies were found, along with the home of Mr Huntley and Ms Carr, and the primary and secondary schools where he worked.
Teams were also scouring the home of Mr Huntley's parents, Kevin and Lynda, in the village of Littleport.