Officials are close to finding the cause of Heath Ledger’s untimely death and reports reveals that it is possible that Brokeback star may have died from natural causes. Sources close to the investigation to the star’s death say the level of toxicity from medication in his system was low enough not to have killed him. The insiders say Heath's heart stopped and he may have died from a heart attack despite being aged just 28, according to website TMZ.com. The reports emerged as Heath's heartbroken family held a private memorial service for him in Los Angeles on Saturday. It is also claimed authorities suspect the Australian actor was dead for about three hours before he was found in the bedroom of his New York apartment. And it is not believed that the housekeeper who found him heard him snoring at about 1pm, TMZ.com says. A fireman on the scene reported a case of rigor mortis in Heath’s jaw shortly after arriving at 3.30pm Authorities are understood to be furious at reports there may have been a "sinister plot" to remove illegal drugs from Heath's apartment before police and medics arrived. Sources told TMZ.com it would have been "impossible" for a bodyguard sent to the apartment by Heath's close friend Mary-Kate Olsen to have taken anything away without cops noticing. They say officers were there the entire time the bodyguard was present. Heath's body is being flown back to his home city of Perth in Australia, where he will be laid to rest. There are reports his funeral service could be held at his former school, Guildford Grammar. Picture: Anthony J. Causi / Splash News