A Russian entrepreneur suspected of embezzling money earmarked for building military submarines was raped, tortured, and killed in pretrial detention, the independent newspaper Novaya Gazeta reports.

In an April 16 report that cited what it said were the findings of state forensic pathologists in St. Petersburg, Novaya Gazeta said that Valery Pshenichny's jailers "tortured and then killed him" and "did not even try to hide the evidence."

The forensics experts "ruled out suicide" and determined that Pshenichny -- who was found hanging in his cell on February 5, three weeks after his arrest -- was raped before his death, the newspaper reported.

It cited the forensics experts it said had completed an autopsy last week as saying that electric shock burns from a water-boiler cord were found in his mouth, lacerations and stab wounds found on his body, and his spine was broken.

Prison authorities have taken issue with the report -- which is likely to deepen rights activists' concerns about the treatment of inmates in Russian prisons and pretrial detention facilities -- but do not appear to have issued a direct denial.

In a statement on April 17, the regional branch of Russia’s corrections agency, the Federal Service for the Implementation of Punishment, said that reports claiming Pshenichny died a violent death were based on "unverified information from unofficial sources."

The statement said that the "preliminary diagnosis" reached after Pshenichny's death was suicide by asphyxiation, and that the authorities cannot disclose details while investigations continue.

The administration of the pretrial detention center where he was held also said after his death that he had committed suicide.

Friends and colleagues of Pshenichny, 56, sometimes called him Russia's Elon Musk because he developed a unique modeling technology for submarine construction and repair, according to Novaya Gazeta.

He was suspected of embezzling 100 million rubles ($1.6 million) from a 2015 project on the construction of military submarines for the Russian Defense Ministry.

Pshenichny was prosecuted after he began to suspect his business partner Andrei Petrov of embezzlement and reported him to law enforcement, Novaya Gazeta reported.

Petrov was arrested but released after he testified that Pshenichny himself and another associate had conspired to inflate the cost of the Defense Ministry contract.

Before his death in custody, Pshenichny managed to send three written messages to his wife urging her not to "pay anything to anyone," the newspaper reported.

It said his widow and friends believe the messages were an indication that somebody was trying to extort money from him.

With reporting by Novaya Gazeta and the Moscow Times