A fishing boat used to kidnap three crew members of a Japanese tugboat had also been hijacked by pirates, Malaysian police said.
Crew members of the boat who were questioned by police said they were released by the pirates on Thursday.
Their boat docked at a port at Hutan Melintang in Perak, adjacent to Penang.
According to police, the fishing boat was hijacked on Sunday, a day before pirates attacked the Japanese-registered tugboat Idaten in the Malacca Strait and abducted two Japanese and a Filipino.
The fishing boat crew told police the pirates threatened them with guns and stole 2,000 ringgit (about 55,000 yen), 2,000 liters of fuel and even the fish the crew had caught.