Russia's main opposition newspaper Novaya Gazeta on Wednesday said its top journalist had fled the country after the country's chief investigator threatened to kill him.
The newspaper's editor Dmitry Muratov said in an open letter that the head of the Investigative Committee, which probes major crimes, had threatened its deputy editor Sergei Sokolov over an article criticizing a high-profile case.
Contacted by AFP Wednesday, Muratov said Sokolov "had been forced to leave the country" and that he could not be reached by telephone.
The Investigative Committee declined to comment when contacted by AFP.
Novaya Gazeta is jointly owned by Alexander Lebedev, who also owns Britain's Evening Standard and The Independent newspapers, and the last Soviet leader Mikhail Gorbachev.
"You brutally threatened the life of my deputy editor," Muratov wrote in his open letter to Investigative Committee chief Alexander Bastrykin.
"You even joked that you would be the one investigating the (murder) case."
The journalist and the investigator allegedly quarreled on a trip they took together last Monday, Muratov wrote in the letter, published on the newspaper's website.
After coming back to Moscow, Bastrykin's "security guards put Sokolov into a car and took him to a forest in the Moscow region" where the official made the threats, Muratov wrote.
Five journalists were detained Wednesday afternoon as they attempted to picket the Investigative Committee building, Moscow Echo radio station reported, naming four as being on its staff.
"It was a good decision if Novaya Gazeta took Sokolov out of the country," the station's chief editor Alexei Venediktov wrote on Twitter.
Bastrykin's threats concerned an article published on June 4 in which Sokolov lambasted Bastrykin for an overly light punishment given to a man convicted of covering up a 2010 mass murder, Muratov wrote.
Twelve people, including children, were brutally killed in the southern town of Kushchevskaya in a crime blamed on fighting between clans. The man convicted of helping conceal the crime kept his freedom and was recently fined 150,000 rubles ($4,600).
Novaya Gazeta, a tri-weekly paper known for its investigative reporting and flagrant opposition to President Vladimir Putin, has lost several journalists in unresolved murders over the past decade.
In 2006, its top investigator Anna Politkovskaya was gunned down in her apartment building in a case that shook the world and is still being investigated with no one punished over five years later.
The website of Novaya Gazeta has crashed periodically since Tuesday morning when the editors reported a hacker attack on the day of a mass protest in Moscow.