Moscow (CNN)Ever since Vladimir Putin came to power, there have been killings of politicians, of human rights activists, of journalists. Boris Nemtsov, one of Russia's most prominent opposition figures, is only the latest victim. The key thing all these crimes have in common is that none of them get properly resolved. Of course, the Kremlin will issue condemnation and condolences, as it has done over the assassination of Nemtsov. But the killers and the people who ordered the killings don't usually end up facing justice -- and if you are an opposition politician in Russia, or a human rights activist, or a journalist, you will know this. If the dangers weren't clear enough, the circumstances of the most recent killing are a stark reminder. It was late Friday night. Boris Nemtsov and his girlfriend Anna Duritskaya, a Ukrainian model, had eaten dinner at plush restaurant on Red Square. Afterwards, despite the chilly weather, they decided to walk back to his apartment, perhaps to take in the stunning views. The Kremlin looks spectacular at night. It was on this short journey, in the heart of Moscow, that the gunman struck, leaving Nemtsov dead within sight of the red Kremlin walls -- walls which, by the way, bristle with security cameras. In the days since, thousands have made pilgrimage to the place where the outspoken Putin critic was shot to pay their respects, leaving a mountain of flowers and personal messages. An opposition rally on Sunday, which Nemtsov was meant to lead, was canceled and replaced with a mourning march past the crime scene. It was the biggest pro-opposition rally in the Russian capital for years. But few who took part could have missed the symbolism, the real message the killers -- whoever they are -- sent by gunning down such a prominent Kremlin critic in the shadow of its towering walls. It's this: if you oppose the Kremlin, if you criticize its power, if you stand for greater democracy and reform, as Boris Nemtsov did, this could happen to you too. It's hard to predict what impact this message will have. "Yet another terrible page has been turned in the history we all share," wrote Mikhail Khodorkovsky, the once-jailed oligarch-turned Kremlin critic now in exile. "What the next page holds is up to each and every one of us," he said, commenting on the death of Nemtsov. The statement was issued under the banner "We Are Not Afraid". But many Russians I've spoken to since the killing are, in fact, very afraid. And while the hope among opposition activists is that Nemtsov's killing may at least invigorate their ranks, one very real possibility is that it will do the exact opposite: further silence an already very quiet minority opposed to the rule of Vladimir Putin.
A series of Kremlin critics have been murdered since Vladimir Putin came to power . The killing of Boris Nemtsov has struck fear into the hearts of Putin's critics .