Radiation expert, 46, who investigated the 'assassination' of KGB spy Alexander Litvinenko 'killed himself by stabbing his arms and chest repeatedly five months after a trip to Russia'

A radiation expert who investigated the 'assassination' of Alexander Litvinenko was found dead five months after a trip to Russia, an inquest heard.

Father-of-two Matthew Puncher, 46, bled to death at his home from multiple
stab wounds inflicted by two knives.

A pathologist said he could not ' exclude' the possibility that someone else was involved in the death - but concluded the injuries were self-inflicted.

It led a coroner to record that Dr Puncher - who discovered the amount of toxic polonium inside ex-KGB agent Litvinenko after he drank poisoned tea in London in 2006 - committed suicide.

The inquest also heard the scientist had 'become obsessed' with a coding error he made in his research which he feared could 'land him in prison' for breaking a contract with the US Government, while his wife said his mood had 'completely changed' following a trip to Russia.

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

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

He had been given sole responsibility over a contract with the US Federal Government for a programme measuring polonium levels inside people who previously worked on the USSR's nuclear weapons. 

Head of department at Harwell, George Etherington, described Dr Puncher's concerns that his 'miscalculation' of the effects of the radiation on the workers would land him prison as 'irrational'.

The inquest also heard that redundancies and restructuring at Public Health England's premises in Harwell, near Didcot, had resulted in Mr Puncher receiving a much greater workload.

Colleague George Etherington said in a statement that Dr Puncher was a senior scientist working in the area of radiation exposure.

He said: 'About three to five years ago we began to carry out contractual work for the American Federal Government working on risks of exposure to plutonium.

'About two to three years ago Matt was asked to take the lead and in April 2015 the restructuring was completed,' he said.

'In February 2016 he attended a meeting in Russia and when he returned he appeared to be quiet and more confined and people told me mistakes made in mathematical analysis came to light during this meeting.

'On April 27 I could see Matt was stressed and he said he had made a mistake and he thought he could be prosecuted for not meeting the contractual commitment.

'He said it was having an effect on his marriage but said his wife was very supportive but he had been having thoughts of suicide. I told him his fears were groundless and he would look back and wonder why he worried so much.'

The inquest heard Dr Puncher had told other workers about the error in his paper which was rectified in an addendum but that was something he believed was a way of 'fudging it.'