DNA test results have cleared five men from suspicion that one of them could be a serial rapist who has attacked 10 women, most of them in their 70s.
"Five suspects have already undergone DNA tests but their DNA did not match that of the attacker," Office of Police Forensic Science acting commissioner Pol Lt General Manu Mekmok said yesterday.
Manu said police believe a serial rapist may be responsible for 10 rapes between 2010 and this year. Two of the victims were also killed.
DNA test results for seven rapes - including a sexual attack early on Sunday - have confirmed the rapist was the same man. The results for other cases will be available soon.
Manu said the 10 rape cases had some similarities. For example, they happened in the wee hours and clear fingerprints and footprints of the attacker were found at each scene.
The Criminals Database Operating System has, so far, not provided any match for fingerprints of the serial rapist that police took from crime scenes.
"We have checked with the database in our bid to solve these cases fast," Manu said.
Meanwhile, director-general of the Mental Health Department, Dr Jedsada Chokdamrongsuk, said his department would help analyse the mental condition of the serial rapist if requested by police.
"Available information suggests he does not suffer psychosis. But he may have paraphilia (an atypical sexual perversion) or just sexual preferences," he said.
Jedsada revealed that he had already instructed the Galya Rajanagarindra Institute, which is under his department's supervision, to prepare a diagnosis if police make a request.
The institute's director, Taweesin Visanuyothin, suggested that the serial rapist might have a form of gerophilia, or sexual attraction toward a much older person.
Asked whether gerophilia could be grounds for a penalty reduction if the man is caught, Taweesin said the focus would be on the motives for the attacks, plus other relevant factors such as the murders of victims.
Taweesin said treatment programmes were available for people with gerophilia, including behavioural therapy and psychotherapy.