Five Thai police officers were killed when a small plane crashed into the sea during a parachute training drill on April 25.
The crash occurred around 8:00 am (0100GMT) off the coast of Prachuap Khiri Khan province south of Bangkok.
Police spokesperson Archayon Kraithong said five of the six officers on board were killed, while the sixth is in hospital with serious injuries.
Authorities are examining the aircraft's black box data recorder to determine the cause of crash.
Local media reported the aircraft went down about 100 metres from the shore in Cha-am district, a popular weekend getaway around 130 km (80 miles) southwest of the capital.
Footage shared on social media showed the plane spiralling before plunging into the sea, with people wading through chest-deep water to reach the site.
Police chief Kitrat Phanphet pledged a full investigation.
"The Royal Thai Police express their deepest condolences to the brave officers who lost their lives," the statement said.
