After reviewing investigative files on the case, detectives said they had a list of persons of interest, The Daily Telegraph reported. Detective Chief Superintendent Hamish Campbell, who heads the Homicide and Serious Crime Command, said the review found "investigative and forensic opportunities."
Madeleine disappeared shortly before her 4th birthday in August 2007. She was sleeping with siblings in her parents' holiday apartment in the Portuguese beach resort Praia da Luz while her parents ate at a restaurant within sight of the building.
The case remains unsolved, and investigators do not know if Madeleine is alive or dead. Prime Minister David Cameron ordered the review in London in 2011.
A spokesman for Kate and Gerry McCann said they were "pleased" by the review and did not want to comment on an ongoing investigation. Both parents are doctors with Gerry McCann a cardiologist at a Leicester hospital.
Campbell said Madeleine's abductor might be someone Portuguese police have already interviewed.
"We have to ask ourselves why are cases unsolved and, on many occasions, we find we passed the suspects by already and the suspect sits within our system," he said. "The purpose of the review was to look at the case with fresh eyes and there is always real benefit in doing so."