London police focused on the southern Caribbean for a serial rapist believed to have attacked nearly 100 elderly women and men in Britain, a forensic scientist said Thursday.

British forensic specialist Ray Fysh said scientists used an advanced form of DNA testing to identify the rapist's ancestral blood lines. Based on the results and the fact that there are gaps between the attacks, police believe he might divide his time between the southern Caribbean and England.

"He is probably British," Fysh said. "But it is clear to us that our suspect has ancestry from the southern Caribbean, anywhere from Dominica in the north down to Trinidad in the south."

Fysh was in Trinidad with London police, who have brought their search to the Caribbean. They will travel to Barbados on Saturday to meet with police and devise strategies for catching the man sought for more than a decade.

Police say the suspect has sexually assaulted 88 elderly women and 10 elderly men in southeast London since 1990. The attacks have often been separated by several years, said London police Detective Superintendent Simon Morgan.

"That shows he could be traveling outside of Britain during those periods, perhaps to the Caribbean," Morgan said.

According to a police profile pieced together from interviews with victims, the suspect is an Afro-Caribbean man in his late 30s. He is tall, athletic, and has lived in south London or the south coast city of Brighton for some time, Morgan said.

"We will know if we have the right guy. If the DNA doesn't match, we'll let him go," Morgan said.

London police have offered a $75,000 reward for information leading to the suspect's arrest and conviction.