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The radiation expert who discovered the poison that killed Alexander Litvinenko "committed suicide" by stabbing himself repeatedly with two knives months after a trip to Russia, a coroner ruled.

Matthew Puncher, 46, bled to death at his home after receiving multiple stab wounds across his body from two kitchen knives, an inquest heard.

A pathologist said he could not completely exclude the possibility that someone else had been involved in the death of the father, but came to the conclusion that the injuries were self-inflicted.

But one detective claimed she didn't think he could have done so much damage to himself without falling unconscious.

A coroner recorded that Dr Puncher, who discovered the amount of polonium inside Litvinenko after he drank poisoned tea in London in 2006, committed suicide.

Dr Puncher was an expert in radiation protection dosimetry and worked for Public Health England at the UK's Atomic Energy Research Establishment at Harwell, Oxon.

He had been given sole responsibility over a contract with the US Federal Government for a programme measuring polonium inside former USSR nuclear weapons workers.

(Image: Getty Images)

His wife Kathryn and work colleagues told an inquest into his death that he had "become obsessed" with a mistake he had made in his research.

She also said his mood "completely changed" after a visit to Russia before Christmas.

He was found dead at his home in Drayton, Oxfordshire, in May, with stab wounds to his arms, neck and upper abdomen.

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His body was examined by Home Office pathologist Dr Nicholas Hunt who also conducted the post mortem on weapons expert Dr David Kelly in 2003.

Dr Kelly was found dead in woodland near his South Oxfordshire home, less than 10 miles from where Dr Puncher lived.

The Hutton Inquiry concluded that Dr Kelly had committed suicide.

Detective Constable Rachel Clarke, who investigated Dr Puncher's death, said: "His injuries were so extensive, I didn't know how he could have inflicted them on himself without becoming unconscious so we looked at the wider circumstances."

Pathologist Dr Hunt said it was possible for a person to self-inflict the number of wounds he did before becoming unconscious.

DC Clarke told Oxford Coroner's Court there was no evidence of a disturbance or a struggle and no evidence of anyone else's blood.

And she added: "It was very unusual. All the information told us he was very depressed and no-one in his family seemed particularly surprised he had taken his own life."

Dr Puncher's wife of 16 years, Kathryn said: "He was always an upbeat and sensitive man.

"He was brilliant with the children as he was so intelligent and enjoyed helping them with their homework.

"After Christmas he changed completely. He just lost interest and I had to prompt him to do things like getting dressed and washing up, things he did without thinking before.

"He used to cook all the meals but he just stopped. He seemed to stop caring about anything."

Head of department at Harwell, George Etherington, described Dr Puncher's concerns that his 'coding error' would land him prison for breaking a contract with the US Government as "irrational".

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A colleague also described it as a "minor problem".

Dr Puncher and a colleague calculated the amount of polonimum-210 found inside Alexander Litvinenko's body following his death in 2006.

Litvinenko was a former officer of the Russian FSB secret service who specialised in tackling organised crime.

He fled with his family to London and was granted asylum in 2000 and worked as a journalist, writer and consultant for the British intelligence services.

In January 2016 a UK public inquiry concluded the defector was probably murdered on the direct orders of the Russian security service FSB, approved by President Putin.

Oxfordshire Coroner Nicholas Graham recorded a conclusion of suicide on Dr Puncher.