An MP investigating the death of Dr David Kelly says he is convinced the weapons scientist did not kill himself.
Norman Baker tells BBC Two's The Conspiracy Files he has reached the conclusion Dr Kelly's life was "deliberately taken by others".
Mr Baker has also obtained letters suggesting the coroner had doubts about the 2003 Hutton inquiry's ability to establish the cause of death.
Hutton reached a verdict of suicide but a public inquest was never completed.
Dr Kelly, whose body was found in July 2003, had been under intense pressure after being named as the suspected source of a BBC report claiming the government "sexed up" a dossier on the threat posed by Iraq.
Coroner Nicholas Gardiner opened an inquest into his death in Oxford just a few days after his body was found on Harrowdown Hill.
But he was ordered to adjourn it by the Lord Chancellor, Lord Falconer, as the Hutton inquiry would take over, and it was not resumed.
Lord Falconer said he wanted to minimise the distress caused to the Kelly family.
The official account given by the Hutton inquiry was that Dr Kelly committed suicide by cutting his left wrist, and taking an overdose of the painkiller Co-Proxamol.
In his report, Lord Hutton said: "There was no involvement by a third person in Dr Kelly's death."
Mr Baker, who has spent a year investigating the case, believes there is enough evidence to suggest that the scientist did not kill himself.
The Liberal Democrat MP said toxicology reports suggested there was not enough painkiller in Dr Kelly's system to kill him, and the method he had apparently chosen to commit suicide was not a recognised or effective one.
"I'm satisfied it was not suicide. And after that you're left with the conclusion that his life was deliberately taken by others," he tells The Conspiracy Files.
He tells the programme it has been suggested to him that the weapons scientist was assassinated.
Speaking last week on BBC Radio 5 Live, Mr Baker said he was not ready to reveal all the evidence he has unearthed, but would consider passing a file to the police in due course.
Mr Baker has obtained letters between Mr Gardiner and the Lord Chancellor's office from 2003, suggesting the coroner was not happy with the Hutton inquiry's ability to establish the cause of death.
The letters were given to the MP by Constitutional Affairs minister Harriet Harman and have not been revealed publicly before.
On 6 August 2003 Mr Gardiner wrote to the Lord Chancellor expressing concern about Hutton's lack of legal powers compared with an inquest.
"As you will know, a coroner has power to compel the attendance of witnesses. There are no such powers attached to a public inquiry," Mr Gardiner wrote.
The Oxfordshire coroner also asked to be allowed to continue with the inquest because "the preliminary cause of death given at the opening of the inquest no longer represents the final view of the pathologist, and evidence from him would need to be given to correct and update the evidence already received".
Mr Gardiner met officials from the Department of Constitutional Affairs on 11 August 2003 "to discuss the mechanics of admitting evidence from the pathologist and analyst".
The Lord Chancellor then accepted the coroner's need to have one further hearing.
Lord Hutton was given the job of establishing how Dr Kelly died
In a letter to Mr Gardiner, dated 12 August 2003, Sarah Albon, private secretary to the Lord Chancellor, said that "the cause of death of Dr David Kelly is likely to be adequately investigated by the judicial inquiry conducted by Lord Hutton".
It said Lord Falconer accepted Mr Gardiner may want to take fresh evidence from the pathologist and analyst.
But he was "most anxious to avoid any unnecessary distress to the family, and has asked that you keep the proceedings as short as possible and, so far as the Coroner's Rules allow, take the evidence in writing".
The coroner did just that in a hearing on 14 August 2003.
On 18 August 2003 a death certificate was registered setting out the causes of death.
Yet the Hutton inquiry had only just started taking evidence and its report was published a full five months later.
In March 2004, a final hearing was held in Oxford at which Mr Gardiner said he was satisfied there were "no exceptional reasons," including concerns about the Hutton inquiry's powers, for the inquest to be resumed.
The Conspiracy Files explores a number of alternatives as to how Dr Kelly might have met his end.
A former colleague of the weapons inspector, former UN weapons inspector Richard Spertzel, tells the programme he believes the scientist was murdered by the Iraqis.
Mr Spertzel, who was America's most senior biological weapons inspector and who worked alongside Dr Kelly for many years in Iraq, believes the Iraqi regime may have pursued a vendetta against Dr Kelly.
"I believe that David was probably a victim of Iraqi Intelligence Service because of long standing enmity of Iraq towards David," he says.
"A number of us were on an Iraqi hit list. I was number three, and my understanding, David was only a couple behind that.
"And none of the people on that hit list were welcome in Iraq. Immediately after David's death, a number of the other inspectors and I exchanged emails saying, 'Be careful.' "
The Conspiracy Files is on Sunday, 25 February, at 2100 GMT on BBC Two.