They came for Dmitri Kolker, an ailing physicist, in the intensive care ward. They came for Ivan Fedotov, a hockey star, as he was leaving practice with a film crew in tow. They came for Vladimir Mau, a state university rector, the week he was re-elected to the board of Gazprom.

The message sent by these high-profile detentions: Nearly anyone is now punishable in Vladimir V. Putin’s Russia.

The flurry of arrests across the country in recent days has signaled that the Kremlin is intent on tightening the noose around Russian society even further. It appears to be a manifestation of President Putin’s declaration in the early weeks of his war in Ukraine that Russia needed to cleanse itself of pro-Western “scum and traitors,” and it is creating an unmistakable chill.

“Every day feels like it could be the last,” Leonid Gozman, 71, a commentator who continues to speak out against Mr. Putin and the war, said in a phone interview from Moscow, acknowledging the fear that he, too, could be arrested.
None of the targets of the recent crackdown was an outspoken Kremlin critic; many of the loudest Putin opponents who chose to stay in Russia after the invasion of Ukraine, like the politicians Ilya Yashin and Vladimir Kara-Murza, were already in jail. But each of the recent crackdown targets represented an outward-looking Russia that Mr. Putin increasingly describes as an existential threat. And the ways they were taken into custody appeared designed to make waves.

Mr. Kolker, the physicist, entered the hospital in the Siberian city of Novosibirsk last week for treatment for late-stage cancer, so weak that he was unable to eat. The next day, agents for the Federal Security Service, or F.S.B., the successor agency to the K.G.B., arrived and, accusing him of treason, flew him to a Moscow jail. Over the weekend, he died in custody.

“The F.S.B. killed my father,” his son Maksim, 21, wrote in all capitals on social media alongside an image of the three-line telegram sent by the authorities to notify the family of the death. “They didn’t even let our family say goodbye.”

Maksim Kolker, who is following in his father’s footsteps as a physicist in Novosibirsk, said Dmitri Kolker had been known for hiring students to work in his laboratory, helping persuade some budding Russian scientists not to seek work abroad.

Now, he said in a phone interview, the family has to return Mr. Kolker’s body from Moscow at their own cost.

It was unclear why the F.S.B. targeted Dmitri Kolker, 54, a specialist in quantum optics. State media reported that he had been jailed on suspicion of passing secrets abroad. But critics of the Kremlin say it is part of a widening campaign by the F.S.B. to crack down on freedom of thought in the academic world. Another Novosibirsk physicist who was also arrested on suspicion of treason last week, Anatoly Maslov, remains in custody.

The arrests came at the same time as the arrest on fraud charges of Mr. Mau, a leading Russian economist who is the head of a sprawling state university, the Russian Presidential Academy of National Economy and Public Administration.

Mr. Mau, 62, was in no way a public critic of the Kremlin. He had joined more than 300 senior academic officials in signing a March open letter calling Russia’s invasion of Ukraine a “necessary decision,” and he was re-elected to the board of Gazprom, the Russian energy giant, just last week. But he also had a reputation as what scholars of Russian politics call a “systemic liberal,” someone who was working within Mr. Putin’s system to try to nudge it in a more open and pro-Western direction.

“A big enemy of the government and the stability of the government are people who carry knowledge,” said Mr. Gozman, who worked with Mr. Mau as a government adviser in the 1990s. “Truth is an enemy here.

“In education, it is important that a person actively profess and share the values that he has to implant in the heads of his students,” said Ms. Schulmann, now a fellow at the Robert Bosch Academy in Berlin. “Here, ambiguous loyalty may not be permitted.”

Mr. Putin has said as much himself. In the speech in March in which he railed about the traitors in Russia’s midst, he called out those who physically reside in Russia but live in the West “in their thoughts, in their slave-like consciousness.”

He is also increasingly asserting that truly patriotic Russians must be committed to living and working in Russia. He told an economic conference in St. Petersburg last month that “real, solid success and a feeling of dignity and self-respect only occurs when you tie your future and your children’s future to your Motherland.”

In that context, the news that Mr. Fedotov, the goalie of Russia’s silver-medal national hockey team at the Beijing Olympics this February, signed a contract in May with the Philadelphia Flyers was likely to have been seen as a challenge.

Mr. Fedotov, 25, one the hockey world’s up-and-coming stars, was planning to leave for the United States this month, according to Russian media reports.