Two more people have come forward claiming to be victims of abuse at the former Haut de la Garenne children's home in Jersey, police say.
Forensic officers are examining areas of Haut de la Garenne
At a news conference outside the building, Deputy Police Chief Lenny Harper said they had made "allegations of serious sexual crimes".
He also said a makeshift trap door had been found leading to the building's cellars, which police are searching.
A child's skull was found at the site on Saturday.
"We've had two people in the last few hours who have come forward and reported extremely serious allegations of crime to us that are alleged to have happened in here", Lenny Harper told journalists.
"[The] team have also uncovered what we've been referring to, or what some of the witnesses have referred to, as a trap door when they've been talking about offences that were committed in that cellar area", he said.
"It is in effect a space in the floor boards but the existence of it and the location of it again corroborates what some of the victims have been telling us."
Mr Harper said his officers were grateful for the increasing amount of help they were getting from the public.
But he said that had meant an increased workload, and he had requested 12 more investigators to join officers already working at the scene.
He told journalists that the chief minister of Jersey had given his assurance that all necessary resources would be put at the disposal of the investigation.
A sniffer dog reacted "strongly" when it entered the underground room on Wednesday, according to officers.
A forensic archaeologist has been sifting through large piles of rubble and soil in the cellar.
Mr Harper said a second underground room adjoining the first had still to be searched. It is understood to be the same size as the first - about 12ft square and 8ft high - and also bricked up.
He said police were determined not to destroy vital clues by hurrying their search of the first room in order to get to the next. "Every ounce of evidence" would be collected.
Some 160 people have said they were abused at Haut de la Garenne.
House parents' statement
Tony and Morag Jordan, of Kirriemuir, in Angus, Scotland, who worked as house parents at Haut de la Garenne from 1971 to 1984, have insisted they have "nothing to hide".
In a statement issued through their solicitors, the couple said they would help police with their inquiries.
The former Haute de la Garenne home care home and Jersey Sea Cadets are the main focus of an investigation into the sexual and physical abuse of boys and girls between the ages of 11 and 15 dating back over several decades.