A top nuclear scientist found stabbed to death after returning from a research trip to Russia was given an official briefing before he travelled and was not judged to be in any danger, the British government has declared.

The body of Dr Matthew Puncher was found riddled with knife wounds in 2016, weeks after his nuclear research helped a judge determine that the KGB defector Alexander Litvinenko had been poisoned in London by Russia’s secret service – and shortly after he visited the country on separate government business.

The police and coroner declared Puncher’s death a suicide – concluding that he had managed to stab and slash himself repeatedly with two separate knives before succumbing to his wounds. But BuzzFeed News last year revealed that US intelligence agencies had passed MI6 evidence connecting Puncher’s death – and 13 others – to Russian state or mafia assassins, yet the police had treated every case as non-suspicious.

The government denied failing in its duty of care towards Puncher in a letter to Lord Rooker, a Labour peer who wrote to Theresa May in November asking why the scientist had been sent to Russia on state business in the immediate aftermath of the Litvinenko verdict. “It was known how explosive the issue was between the UK and Russia, so why was Dr Puncher not withdrawn?” he asked, noting that the prime minister had made public her commitment to “the population being kept safe” and yet “it appears the Government failed in respect of Dr Puncher”.

Lord Rooker received a response last week noting his concerns but insisting that the government had no reason to believe Puncher was at risk when he was assigned to visit the Mayak nuclear facility in Russia to study the effects of long-term radiation exposure on the local population.

Steve Brine, the parliamentary under secretary of state for public health, wrote that Puncher had been “properly briefed” before his visit and “there was no extant risk considered or known of to give cause for concern”. He added: “It goes without saying that we were profoundly sad to learn of the death at such a young age of Dr Puncher, a dedicated and highly valued public servant, and we extend our sincere condolences to his family, friends and colleagues.”

Lord Rooker told BuzzFeed News the government had not provided enough information in its letter to determine how carefully the risks of the Mayak visit had been assessed – but said it appeared from the response that any consideration given to Puncher’s safety in the aftermath of the Litvinenko verdict had been “very, very superficial”.

