Mark Bridger, the man detained after the abduction of April Jones, has been arrested on suspicion of the murder of the missing five-year-old, police said today.
Police announced at a press conference in Aberystwyth that the 46-year-old - arrested on Tuesday on suspicion of abduction - is now being held on suspicion of murder.
Bridger continues to be held at Aberystwyth police station.
At the press briefing, the public were told it would "no longer be appropriate" for untrained volunteers to continue with the search.
The grim news was revealed by Detective Superintendent Reg Bevan at a press conference in Aberystwyth.
He said: "Mark Bridger has been arrested on suspicion of the murder of April Jones.
"He remains in custody at Aberystwyth Police Station where he continues to be questioned.
"The arrest does not detract from our efforts to find April and we remain committed to finding her.
"Her family has been informed of this development and as you would expect they continue to be supported by a family liaison officer.
"While this is a significant development in the investigation, I once again appeal to the public for information which may help us find April.
"We are looking to trace the movements of Mark Bridger between 6.30pm on Monday and 3.30pm on Tuesday and any sightings of him between these times.
"We also need information regarding the movements of the blue Land Rover Discovery registration L503 MEP between these times."
Superintendent Ian John acknowledged again that volunteer searchers had played a "vital part" in the hunt for April so far.
But the dynamic has changed with the announcement that Mr Bridger is now being held on suspicion of murder, he said.
Searches will continue but the focus has inevitably changed from looking for a live child to one of looking for a body.
The brief press conference in Aberystwyth this morning was in stark contrast to the upbeat approach of many residents yesterday.
In response to an appeal from mother Coral Jones to "wear a pink ribbon for April", residents had acted quickly to show their solidarity.
The act of united faith was the community's way of showing April's family that no-one had given up hope of finding her alive.
Today Mr Bevan spoke only briefly to reveal the dramatic development.
Looking tired and drawn himself on the fifth day of searching, he renewed the appeal for information regarding Mr Bridger's movements.
One of the world's leading forensic psychologists who advised British and Portuguese police in the search for Madeleine McCann is reportedly helping detectives in the case.
Joe Sullivan is said to have been drafted into the Dyfed Powys police investigation team to give advice on interviewing Mr Bridger, The Times claimed.
Small expert teams have continued to comb areas of thick forest in the mountains around the town of Machynlleth in mid-Wales.
Their efforts are being driven by the unwavering support that is coming in not just from the surrounding community but across the UK.
Prime Minister David Cameron added his voice to the chorus of appeals for anyone with the smallest piece of information to come forward.
He described the ongoing ordeal as "every family's nightmare" and urged people to "talk to the police".
"My heart just goes out to April's family," he said. "This is every family's nightmare, having this happen, and the fact that she suffers from cerebral palsy, something I know a little about from my own children, only makes this worse."
His words follow Mrs Jones's emotional plea yesterday for help from anyone with information.
April's older sister, Jasmine, 16, also spoke for the first time tonight, telling Sky News: "I just want our beautiful princess home now. It's been too long.
"Knowing someone knows something but won't say it makes me feel even worse."
Elsewhere, parents at April's school have praised the sensitive way in which teaching staff have handled the abduction.
Classmates at the primary school April attends on the estate where she lives were told on Tuesday that she is missing.
The news, revealed to children too young to understand its significance, was linked to warnings of stranger danger.
In response to Mrs Jones's call for residents to wear pink, the school has been festooned with a large pink ribbon.
Several metres long, it is intertwined the length of a wrought iron barrier at the entrance to the school.
While the heartening support of the community is undoubtedly helping April's family cope, residents believe life in the area will never be the same again.
Confidence that children are safe to play out unattended has been shaken to the core.
Many believe life in the community, whatever the outcome of search efforts, will never return to the peace of the past.
Even in the tiny hamlet of Ceinws, where Mr Bridger's rented house stands, residents are struggling to comprehend the events of Monday evening.
Villager Carl Utteridge, 76, spoke to Mr Bridger while waiting for a bus several weeks ago.
"He didn't say much. It's unbelievable to anyone here. You just don't expect it," he said.