Russian investigative journalist Maksim Borodin of Yekaterinburg has died of injuries sustained on April 12 when he fell from the window of his fifth-floor apartment.

Borodin, 32, died on April 15 in a hospital without recovering consciousness. Officially, his death was being investigated as a suicide.

A Sverdlovsk Oblast police spokesman said it was "unlikely that this story is of a criminal nature."

He said the door to Borodin's apartment was locked from the inside and there was no sign of forced entry. He added that the keys to the apartment were found inside and no suicide note has been found.

Polina Rumyantseva, the editor in chief of Novy Den, where Borodin worked, said the same day that she did not believe Borodin committed suicide.

A friend of Borodin's, Vyacheslav Bashkov, wrote on Facebook on April 15 that Borodin contacted him at 5 a.m. on April 11 and said his building was surrounded by "security forces" wearing camouflage and face masks.

He said that Borodin was alarmed, but not hysterical or drunk. Borodin reportedly said that he believed his apartment was about to be searched and that the security officers were waiting for a court order. He asked Bashkov to find him a lawyer.

An hour later, however, Borodin called back and said he had been mistaken and that the security officers were conducting some sort of drill.

"I didn't call him after that," Bashkov wrote, "although I was waiting for him to write something on Facebook. But he didn't write anything and on the 13th the media reported that Maksim had been found under his balcony and he was in the emergency room."

Borodin regularly wrote on crime and corruption. In recent weeks, he wrote extensively about the deaths in February of Russian mercenaries fighting in Syria, identifying several fighters from the Urals city of Asbest who had been killed.

On February 7, a group of Russian mercenaries with tanks and artillery attacked territory held by U.S.-backed opponents of the government of Syrian President Bashar al-Assad.

The U.S.-led international coalition responded with air strikes that are believed to have killed dozens of Russian fighters.

According to some media reports, more than 200 Russian mercenaries died in the incident, although the Russian government has not confirmed the casualty toll.

With reporting by Novy Den, RIA Novosti, and Grani.ru