A senior police detective was told to play down the death of Russian whistleblower Alexander Perepilichnyy to the media, a confidential police report reveals.

The financier, who fled to the UK after helping to expose a massive Kremlin-linked fraud, collapsed and died while jogging outside his home in Surrey in November 2012.

British police insist that he died of natural causes, but BuzzFeed News revealed last June that US intelligence officials believed with “high confidence” that he was the victim of a Russian assassination plot — one of 14 suspicious Russia-linked deaths in the UK.

On Monday, coroner Nicholas Hilliard QC, who is overseeing an inquest into Perepilichnyy’s death, released a cache of documents, including police and witness statements, emails, and minutes of meetings between senior police officers involved in the investigation. The material was released following a court application made by BuzzFeed News last year arguing they could be key to public understanding of the case.

The minutes, redacted and only partially released, show that in special meetings held soon after Perepilichnyy’s death, the senior officers discussed how to handle questions from journalists and MPs about it. Olivia Pinkney, then Surrey’s assistant chief constable, told the officer leading the investigation, detective superintendent Ian Pollard, to work with the force’s media department “and make it a non issue”.

At the time, police considered Perepilichnyy’s death to be “unexplained and under investigation”, after an initial postmortem proved “inconclusive”.

Despite her instruction to play down the death with the media, the same minutes show that Pinkney also criticised how thoroughly Surrey police looked into his alleged links to the Kremlin-linked fraud. She outlined three “missed opportunities to raise the death as a concern/issue to senior management within Surrey police”.

One was the force’s delay in referring Perepilichnyy’s death to “Special Branch”, or the National Special Branch Intelligence System (NSBIS) — a central database for sharing intelligence across the UK. The inquest previously heard that this database contained information on both Perepilichnyy and his wife, as well as companies connected to them.

Another “missed opportunity” referred to a letter sent to Surrey police a week after his death by lawyers for Hermitage Capital, the firm at the centre of the alleged $230 million Kremlin-linked tax fraud. The letter alerted police to the fact Perepilichnyy was a “whistleblower who had been cooperating with authorities and exposing Russian organised crime.”

Citing the London poisoning of spy Alexander Litvinenko, the letter asked police to investigate his death as a potential murder and asked them to secure the evidence as quickly as possible. Bill Browder, Hermitage’s chief executive, previously told the court that the police repeatedly failed to respond to or acknowledge the letter.

The third “missed opportunity” was a phone call from the Independent, which broke the story of his death, asking questions about the investigation.

Emails between Perepilichnyy and life insurers Legal & General reveal that shortly before he collapsed, the financier took out insurance for “family protection purposes” in the event of his “premature” or “untimely” death. His wife had previously told the inquest that her husband had taken out the multimillion-pound insurance policies to help secure a mortgage for an expensive property they wanted to buy.

A Surrey police spokesperson said it would be “inappropriate to comment any further while the coronial process is continuing”.

The inquest into Perepilichnyy’s death is ongoing and expected to hear closing submissions at the Old Bailey in September 2018.