News reports have said the Indonesians were killed on March 9 after boarding the Thai fishing boat as part of checks of vessels in Indonesian waters. Their bodies have not been found.
The case has strained relations between Thailand and Indonesia and put pressure on Thailand's fishing industry, which fishes heavily in Indonesian waters. Thai newspapers have reported that Indonesia has cracked down on Thai trawlers by more rigorously enforcing regulations on fishing in its waters.
Pol Lt Gen Chakthip Chaijinda said four fishermen suspected in the killings were found on Thursday on a boat in waters near Thailand's southern Narathiwat province. Three other suspects out of 12 for whom arrest warrants have been issued were arrested last month.
Pol Lt Gen Chakthip said the newly arrested men confessed but insisted they were ordered to act by the ship's captain, who remains at large. He said police found hammers and knives believed to be used in the killings.