Sri Lankan police were Thursday hunting for a fishing trawler believed to have been stolen by its crew in a bid to illegally transport asylum seekers to Australia.
Police said three crewmen and the skipper of the trawler had staged a hijacking on Sunday night to try to cover up the theft of the boat and use it in the highly lucrative people-smuggling business.
"We are investigating this as a theft carried out by the crew," police spokesman Prashantha Jayakody told AFP. "We are keeping an eye on the coast, but if they crossed into international waters, we may not be able to do much."
Police have meanwhile detained for questioning two other crewmen who were picked up by passing merchant vessels after being found bobbing in waters south of the island early on Monday.
The pair had initially told police that the trawler had been attacked by about 40 suspected illegal immigrants carrying swords who arrived in four small boats and overpowered the crew.
"There are conflicting accounts in their statements and it is now clear that this was an inside job to steal the trawler and possibly use it for an illegal journey to Australia," a senior police investigator told AFP.
"We think the skipper of the trawler was involved in the hijacking along with three other crewmen," the officer said, asking not to be named.
"The two who claimed they were attacked appeared to have had a last minute change of heart."
Police said two other trawlers had also been reported missing off the island's southern region since October 2 and they too could have been stolen for people-smuggling.
On Wednesday police arrested another 35 people heading for Australia in a fishing boat, the officer said.
Sri Lankan authorities say they have detained over 1,000 people who have tried to leave for Australia illegally this year.
Australia hopes the prospect of years in detention on remote Pacific islands will deter asylum seekers from attempting the dangerous sea voyage, which has cost hundreds of lives over the past decade.
Sri Lankans pay up to $3,000 for a place on trawlers which take around two weeks to make the treacherous crossing to Australia.