NEW YORK, NY — It's a haunting international murder mystery — involving witchcraft and the human sacrifice of a helpless little boy — that has stumped investigators from London to Nigeria.

Now, stymied Scotland Yard detectives are pinning perhaps their final hopes on New York City's medical examiner to help them crack the case of the child they call Adam.

The boy was slowly and expertly sliced up and beheaded — while still alive.

The mystery unfolded nearly two years ago when the torso of a boy believed to be between 4 and 7 was found in London's River Thames.

The child ingested a potion two days before he was slowly and expertly sliced up and beheaded — while he was still alive, police believe. A sample of the witch's brew, which contains bone fragments, was delivered to the medical examiner's office Wednesday by Detective Constable Mark Ham of New Scotland Yard.

"We don't know who his family is, so we are his family," Ham said.

On the first Christmas after Adam was killed, someone sent him a teddy bear, a gesture that moved battle-hardened Scotland Yard detectives to place the bear in the body bag "so that he wouldn't be alone," Ham said.

Experts here hope to pull DNA from the pinhead-size bone fragments, a process that may yield a particular witch doctor's signature, Ham said.

The potion was a mixture of clay with gold particles, quartz grains and bone, he said.

"These rituals aren't an exact science."

"These rituals aren't an exact science, but we feel that it may very well help us even in interviewing people," said Ham, 41, who was a forensic expert before becoming a cop 12 years ago.

Ellen Borakove, a spokeswoman for the medical examiner's office, declined comment on the case but said the office has advanced DNA extraction techniques, which were used to identify remains from the World Trade Center.

The international investigation began soon after the torso was found floating in the river dressed only in a pair of orange girl's shorts Sept. 21, 2001. The head and limbs have not been found.

Detectives determined that the boy was between 4 and 7, and DNA evidence traced his origin to Benin City, a rural area in southwestern Nigeria, Ham said. British cops, who traveled to Nigeria in search of clues, believe he had been in the U.K. less than 10 days before he was killed.

An evil purpose
Detectives questioned a 31-year-old Nigerian asylum seeker in Scotland after she said her husband was involved in the ritual killing of their children, Ham said.

DNA tests determined that Adam was not her child, and detectives believe the little boy was smuggled into London specifically for the sacrifice.

Police believe the boy was smuggled into London specifically for the sacrifice.

"It's the most horrific thing," Ham said. "What must have been going through that child's head when he was led into the room where they did it?"

Detectives have been hoping to question the woman's husband, who disappeared around the time Adam's remains were discovered, he said. Investigators found clothes in the woman's apartment bought at the same store in Germany as the orange shorts Adam wore.

The woman was deported to Nigeria in November, but she has not been ruled out as a suspect, Ham said.

"This is one that will go down in the Metropolitan Police's history books," he said as he prepared for his trip back to London last night. "It's an investigation I will never, ever forget."