Golunov, who works for the independent website Meduza, was beaten and kept in custody for 12 hours without a lawyer after he was stopped by police in Moscow on Thursday, according to his lawyer. He was transferred to house arrest on Saturday following a public outpouring of support, but he still faces drug dealing charges that could send him to prison for up to 20 years.
The papers dismissed evidence presented in the case against the journalist. Russia's media landscape is fragmented, and such a show of solidarity in the media is rarely seen. All three papers have faced pressure from authorities and covert censorship.
Pavel Chikov, head of the lawyers' association Agora that represents Golunov, on Monday published results of tests that Golunov has taken to prove his innocence. He said the tests indicated that it is unlikely that he regularly handles drugs as police has suggested.
Yevgeny Bryun of the Russian health ministry said on state television on Sunday that lab tests of Golunov's urine did not find any traces of drugs. The circumstances of the journalist's arrest have alarmed the media community. In an apparent attempt to portray Golunov as a professional drug dealer, police on Friday released several photos, reportedly from Golunov's home, of what appeared to be a drugs lab before they retracted the statement, saying that the pictures were taken elsewhere.
Kremlin spokesman Dmitry Peskov told reporters on Monday that President Vladimir Putin is following the case. He expressed confidence that prosecutors will look into possible violations of Golunov's rights, and dismissed suggestion that the police handling of the case undermines public trust in law enforcement agencies.
Journalists and others have protested outside the headquarters of the Moscow police department for four days in a row. Thousands of people have said online that they would take to the streets on Wednesday, a public holiday, to protest Golunov's detention.
Golunov rose to prominence with his investigations into corruption at the Moscow City Hall, the crime-ridden funeral industry and the murky food markets. The journalist told the court on Saturday that he has received threats related to his investigation into Moscow's funeral business.
Meduza's director general Galina Timchenko said on the Ekho Moskvy radio station on Monday that Golunov told her in March about the threats after his piece came out. Timchenko said she had spoken with Golunov about security measures but she could not get Golunov to leave the country.