Nikolay Andrushchenko, 73 and a founder of the privately-owned Novy Peterburg (New Petersburg) newspaper, had been hospitalized since March 9, state news agency RIA Novosti said Wednesday.
Denis Usov, editor of the Novy Peterburg, told CNN that no one knew how Andrushchenko had suffered the injuries that led to his death. But, he said, "it is known that not long before this incident, he was jumped near his house by some unknown individuals, who beat him up and demanded some documents related to his professional work as a journalist, connected with his recent publications."
In the last incident, Andrushchenko was found on the street with a head injury by passersby, Usov said.
"When he was attacked, he was alone," he said. "It is possible that it was an accident, but given that there was pressure on him because of his work before that, we could consider that there is a criminal element to his death."
Andrushchenko was a deputy in the St Petersburg city council in the 1990s, RIA Novosti said. He focused on human rights and criminal matters as a journalist for the newspaper, it said.
In 2008, he was charged with libel, inciting extremist activity, and insulting a government representative, RIA Novosti said. However, the cases were later dismissed.
The Committee to Protect Journalists raised concerns in November 2007
over charges faced by Andrushchenko, saying that it was "apparent that the authorities' actions are aimed at stifling an opposition voice" ahead of a parliamentary election. It also noted that he had been beaten by unknown attackers while on his way home earlier that month.
Boris Vishnevsky, a St Petersburg lawmaker and former contributor to the opposition Novaya Gazeta newspaper, told CNN that Andrushchenko had published some "very harsh reports" but was not one of Putin's more prominent or current critics.
His newspaper has a reputation as being ultranationalist, Vishnevsky said, and does not appear to have a huge readership.
"Of course it's not possible to exclude that the attack on him was somehow connected with his professional activity, but I wouldn't state this as a fact, I hope that an investigation will be carried out," he said.
"Nikolay was not a very easy person. I can say that he was a decent, sincere and honest person, but our political views were always different," he added.