A backbench MP is to investigate the "unanswered questions" from the official inquiry into the death of weapons scientist Dr David Kelly.

The former Liberal Democrat environmental spokesman Norman Baker today revealed his decision to stand down from the shadow cabinet two months ago was based on a quest to establish the "truth" behind Dr Kelly's death.

Mr Baker said he wanted to return to the issue because the 2003 Hutton inquiry had "blatantly failed to get to the bottom of matters".

He vowed to question ministers and to unearth new facts in a bid to establish the "truth" of the case.

Dr Kelly was found dead on July 18 2003 after being named as the possible source of a BBC story on the government's Iraq dossier.

Later that month Lord Hutton was appointed head of an independent inquiry into the events surrounding Dr Kelly's death. After a two-month inquiry, Lord Hutton concluded the scientist had taken his own life.

Oxford coroner Nicholas Gardiner subsequently looked into the possibility of reopening the inquest into Dr Kelly's death, but after reviewing the evidence with the lord chancellor, decided that there was no case for doing so.

Mr Baker explained that he had decided to wait until he relinquished his environmental role before embarking on an investigation to find out the "truth" that the Hutton inquiry had failed to deliver.

"It did not answer questions," he told Guardian Unlimited today.

"It was not carried out using proper rules of evidence, people were not giving evidence under oath and the whole thing became a criticism of the BBC."

Mr Baker said he had given himself a year to carry out his inquiries. This will include revising the medical evidence, interviews with experts and looking at issues relating to the government's "behaviour" in the affair, as well as the weapons of mass destruction claims made in the months preceding Dr Kelly's death.

Mr Baker admitted he already holds a "number of theories" about the scientist's death, but declined to speculate so early into his investigation, which began two months ago just after he stood down from his shadow post.

Mr Baker, who is known for his forensic use of parliamentary questions, insisted his decision to stand down after six years as environment spokesman was his choice alone.

"I have long been unhappy about the sequence of events and I was unhappy at the time about the way the Hutton inquiry was conducted and I wanted to free up some time to look into this," he said.

"I haven't informed the party leadership yet," he added. Asked if Dr Kelly's widow, Janice, was aware of his plans, Mr Baker said: "I recognise the sensitivity of the matter for the family and the need to speak with them, but only if they prepared to do so."