(CNN) -- Police in the Seychelles investigating the deaths of two former U.S. Navy SEALs have video surveillance showing the private security guards enjoying a night out before the men were found dead in a cabin of the Maersk Alabama, a source with knowledge of the investigation tells CNN.
The video led police to two women -- who, the source says, authorities believe to be prostitutes -- seen with the American security guards during the evening. Those women reportedly have identified a location where they say the two men purchased heroin.
Video from several surveillance cameras show the security guards in a restaurant and a casino and on a public street in the Seychelles at night while the Maersk Alabama was in port.
As CNN reported last week, autopsy results indicate the Americans found dead on the container ship on February 18 died of respiratory failure, coupled with suspected heart attacks. Traces of narcotics and hypodermic needles found with the bodies suggested the deaths resulted from drug overdoses, Seychelles authorities said.
Further forensic analysis will be carried out to establish if the two men, 44-year-old Jeffrey Reynolds and 43-year-old Mark Kennedy, had consumed a substance that may have caused their deaths.
"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," according to police.
Toxicology results are not expected for another three weeks, but police spokesperson Jean Toussaint says a criminal investigation continues, and "solid evidence could lead to formal arrests in the deaths."
Toussaint confirmed to CNN that the women seen with the men on surveillance video are cooperating with police, but would not give details on the investigation.
The two men 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 February 18 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.