Throughout the Putin era, it hasn’t been uncommon to see political opponents harassed or even killed.

Anna Politkovskaya was gunned down in 2006 in the elevator of her building in central Moscow after writing several highly praised books detailing the dark side of life in Russia under president Vladimir Putin.

Officials in the United Kingdom protested furiously when, as if out of a Cold War thriller novel, former Russian secret service agent Alexander Litivinenko was apparently poisoned with the radioactive polonium-210 a month later.

Alexei Navalny, who rose to prominence more recently as a critic of Putin and the corruption of Russian government, has been harassed and imprisoned on politically motivated charges.

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Business leaders like Boris Berezovsky and Mikhail Khodorkovsky were exiled and imprisoned after Putin’s government decided that they amassed too much wealth in the fire sale of the 1990s when Putin’s predecessor, Boris Yeltsin, sold many of the former Soviet Union’s public assets.

But the assassination of opposition figure and former Yeltsin-era deputy prime minister Boris Nemtsov is the most brazen attack yet. I’m sure no one will ever be able to tie Nemtsov’s murder to the Kremlin, which is already officially condemning the murder. The attack — an audacious murder on the streets of Moscow when Nemtsov was otherwise on a Friday night stroll — sends a chilling message to everyone in Russia who opposes Putin’s increasingly autocratic rule (not to say that Putin’s rule was even incredibly liberal or democratic).

Nemtsov’s assassination seems certain to subdue a planned opposition march scheduled for Sunday.

Don’t think for a moment that this isn’t exactly the gruesome image the Kremlin wants its critics to see — a dissident gunned down in the back just footsteps away from the Kremlin walls:

Just as Navalny’s imprisonment elevated his credibility among Putin’s critics, Nemtsov’s murder will almost certain transform overnight a liberal opponent with relatively little support and close ties to some of Russia’s more unsavory oligarchs into a martyr gunned down for his anti-Putin dissidence. Though Nemtsov received generally high praise for his work as the governor of Nizhny Novgorod and as a deputy prime minister for a brief period in 1998, his popular appeal was always blunted by association with the painful liberalization reforms of the 1990s.

It wouldn’t be surprising to find that despite Nemtsov’s high-profile work as a Putin opponent in life, he emerges as a greater threat to Putin in death.

He found common cause with chess superstar Gary Kasparov in the late 2000s as dissidents in opposition to Putin-era repression, but Nemtsov was never really the kind of ‘standing-on-the-tank’ figure that Yelstin once was. As Keith Gessen wrote in an expansive piece on the Putin era and its origins for Politico just this week, Nemtsov was never as serious a figure as folks like longtime liberal opponent Grigory Yavlinsky:

Boris Nemtsov, briefly groomed by Yeltsin as his heir apparent, was more interested in maintaining a good tan in winter than vying for political office….

Nemtsov often took controversial stands at odds with the Kremlin. Nemtsov was a critic of Russia’s annexation of Crimea, formerly part of Ukraine, despite wide support among Russians. He was a vocal supporter and adviser to Viktor Yushchenko, the former pro-European president who led the ‘orange revolution’ movement in Ukraine in 2004, despite the Kremlin’s support for opponent Viktor Yanukovych.

There’s already more than a hint that his murder may have been related to Ukraine. News reports state that the woman with whom Nemtsov was walking is Ukrainian, and he vocally opposed Russian military involvement in the fight between Kiev and pro-Russian separatists in eastern Ukraine. That, and the shock factor of the assassination, seems certain to add to tensions between Russia, on the one hand, and the United States other European governments, on the other, as the most recent Minsk plan to bring about a ceasefire between the Ukrainian government and Russian-backed rebels fell apart within hours of its agreement.