(CNN) -- Autopsy results indicate two American security officers found dead on the container ship Maersk Alabama last week died of respiratory failure, coupled with a suspected heart attack, police in the Seychelles said Tuesday.
Further forensic analysis will be carried out to establish if the two men, Jeffrey Reynolds and Mark Kennedy, had consumed a substance that may have brought on these events, a police statement said.
Traces of narcotics were found with the bodies of the officers, it said.
"The police preliminary investigation report includes suspicion of drug use, as indicated by the presence of a syringe and traces of heroin which were found in the cabin," the statement said.
The two men, both 44, worked for Trident Group, a Virginia-based maritime security services firm. Trident Group President Tom Rothrauff said both were former Navy SEALs.
The 500-foot Maersk Alabama was the target of an attempted hijacking in the pirate-infested waters off East Africa in 2009 -- an incident that inspired the 2013 film "Captain Phillips."
The shipping giant Maersk, which hired the Trident Group to guard its ships, said last week that Trident would be conducting random drug tests of its employees.
"Based on our experience with the contractor, this is an isolated incident," Maersk said. But it said new drug tests would start immediately and the company's shore leave policy was under review.
Police said the ship arrived on February 16 in the Seychelles, an archipelago in the Indian Ocean, with a 24-man crew and had been expected to leave two days later. The bodies were found last Tuesday by a colleague who had gone to check in with one of the men in a cabin, Seychelles police said.
The Maersk Alabama has since left the Seychelles capital of Port Victoria.