A mysterious box of Marilyn Monroe documents sealed until 2039 could prove she was murdered by her obsessed psychiatrist, claims a private investigator.

The papers belonged to Dr Ralph Greenson, who found her body and who is suspected by some of administering the barbiturate overdose which killed her in 1962.

Private detective Becky Aldrige found 'Box 29' stored at UCLA library where it will remain sealed to the public for another two decades, despite a list of contents showing it contains a trove of files about Monroe.

Aldrige claims that Dr Greenson killed Monroe after she threatened to reveal affairs she'd had with the Kennedy brothers and he remained haunted by the actress.

The official account says Marilyn Monroe was found dead by Dr Ralph Greenson (left) but private detective Becky Aldrige believes a sealed box of his papers holds answers and that he administered a fatal injection that killed her

'I have always believed Marilyn Monroe was murdered,' Aldrige writes. 'If you look at all of the stories, books, testimonies, and even evidence then there is no reason that Marilyn Monroe's death certificate should not be changed from probable suicide to murder.'

Aldrige has opened a petition asking for the finding of 'probable suicide' to be struck from Monroe's death certificate and for the death to be re-investigated as homicide.

She is asking that the Attorney General speak to two people who she says are alive today and who were never asked to give a statement but 'were present when Marilyn Monroe took her last breath.'

They are LAPD Sgt. Marvin D. Iannone, later promoted to Chief of the Beverly Hills Police Department, and Patrica Newcomb, a friend of Monroe.

According to Aldrige, Newcomb left the country after Monroe's funeral in 1962 and traveled through Europe for six months.

Meanwhile she claims that Iannone dismissed the other officers from Monroe's home on Helena Drive, Brentwood, on the day the screen siren died.

Aldrige says 'time is running out' because Iannone is now 83-years-old and Newcomb is 88.

There have long been conspiracy theories surrounding Monroe's death. The official account says Monroe was found dead by Dr Greenson who broke into her bedroom after being called to the home by the housekeeper in the early hours of the morning.

Medical attendents removing the body of Marilyn Monroe from her home at 12305 Fifth Helena Drive in Brentwood, Los Angeles, in 1962

Monroe had died from acute barbiturate poisoning as a result of an overdose of chloral hydrate and pentobarbital. Due to well-documented bouts of depression and prior overdoses a finding of 'probable suicide' was made by the coroner

Monroe had died from acute barbiturate poisoning as a result of an overdose of chloral hydrate and pentobarbital.

Due to well-documented bouts of depression and prior overdoses a finding of 'probable suicide' was made by the coroner.

However, investigators like Aldrige believe Monroe's alleged affairs with the Kennedy brothers, John F. Kennedy - then President - and his brother Bobby, could provide a motivation for Dr Greenson being asked to give her an overdose.

Aldrige told The Sun that she was stunned to find that Dr Greenson, who died in 1979, had a sealed box of papers.

'I spent hours looking at everything I was allowed to - I couldn't make copies or take pictures so I just took notes,' she told the paper.

Aldrige claims that Monroe's housekeeper Eunice Murray said she became concerned about the light being on in the star's bedroom (pictured: Monroe's home in Brentwood

'I discovered he was obsessed with Marilyn Monroe because he had every book, every magazine, every newspaper that was ever written about Marilyn Monroe, everything.

'Then there were letters that were written to him, people telling him to kill himself because they thought it was his fault, she was dead. I remember thinking "Why did you save this?" ...

'There is also letters in there to Marilyn Monroe from other people - and letters she wrote to other people - why does he even have those? There's also some of his confidential medical files, and another file that doesn't say what it is.'

Investigators like Aldrige believe Monroe's alleged affairs with the Kennedy brothers, John F. Kennedy (pictured) - then President - and his brother Bobby, could provide a motivation for her murder

Aldrige says that in Monroe's previous suicide attempts she had left a note, but on the night of her death there was none.

She also notes mysterious bruises found on Monroe's hips, a common place for injections, but which could also indicate violence.

In addition she claims that Monroe's housekeeper Eunice Murray said she became concerned about the light being on in the star's bedroom.

But even if this had concerned her, Aldrige finds it strange she called Dr Greenson before the emergency services.

Furthermore, she says that Murray had a master key and it would not have made sense for Greenson to break into Monroe's bedroom.

Aldrige also says that Newcombe told her Monroe had a diary at the time of her death but this 'disappeared.'

Aldrige claims that Monroe was killed after threatening to go public about her affairs with the Kennedy brothers.

She claims that an ambulance had arrived at the home but that before she could be taken to hospital Dr Greenson intervened, taking charge of Monroe and giving her a fatal injection.

'The one thing that has never changed in over 53 years is the people involved, the time frame of events and the real manner of death.' Aldrige writes.

'Marilyn deserves this change.'