Ben Judah, writing in the Daily Telegraph:

Vladimir Putin has ruled Russia with three things: money, propaganda and terror. When the Russian economy was booming and the oil price was over $100 a barrel, Putin ruled Russia almost entirely with money – throwing cash at the elites and at the people – with a small dose of propaganda and a tiny injection here and there of terror. Now the money is running out, the equation has shifted. Today, Russia is ruled mostly through propaganda and terror.
Boris Nemtsov took not a step nor a breath that wasn’t under the intense surveillance of the FSB… It is quite simply impossible that this man could have been shot dead without the Kremlin knowing there was a plot afoot to kill him.
This means the murder of Boris Nemtsov was either ordered or allowed to happen: which come to exactly the same thing. That he could be killed like this has shaken the oligarchs and the officers of the Russian elite to their core. Boris Nemtsov was once Russia’s deputy prime minister and a protégé of Boris Yeltsin…His murder means that the Putin’s solemn – and public – promise not to touch Yeltsin and his allies has been torn up.
This means the old Moscow rulebook has been torn up, too. Ever since fall of Khrushchev power in Moscow has changed hands without executions. Once ousted, old ruling cliques were allowed to live their lives out in irrelevance. Ripping this up works perfectly for Putin. Those contemplating, even in the abstract, a coup know they could be executed for it – and those loyal to Putin now believe that they must fight to keep him in power as they could be executed in revenge should he fall. Vladimir Putin now has the elite exactly where he wants them: terrified.

I wonder if that last is true. One of the reasons that full Stalinism never returned to the Soviet Union after the dictator’s death was that the elites decided it was too dangerous for them. Putin has to be careful not to push the elites into thinking that he has become too dangerous/unpredictable not to be opposed. Quite how Judah can be sure—so soon—that this killing has shaken the elite “to its core”, I don’t know, but if he’s right, that might represent more of a danger to Putin than the large crowds bravely protesting today in Moscow.

Writing in the Guardian, Shaun Walker sees things differently to Judah:

Nemtsov’s anti-corruption investigations and criticisms of the Putin regime were scathing, but did not reach many outside the “liberal bubble” of the small urban opposition….
The proximity of one of the Kremlin towers to the spot where Nemtsov was shot in the back is darkly melodramatic, and the symbolism could not be clearer. But this is not the way that the Kremlin has tended to deal with its internal political enemies…thuggish irritations and intimidations, not murder, have been the tools to disarm the opposition.

Note that careful “tended”….

Walker:

Anyone who watches Russian state television – and that includes the vast majority of Russians – will have seen a picture painted over the past year of a victimised Russia attacked by voracious western vultures… According to this narrative, the Russian opposition are traitors, working to destroy the country.
At a recent launch of the Anti-Maidan movement [a pro-Kremlin group] in Russia, the leader of a biker gang, known as “the Surgeon”, who has been photographed many times with Putin, said foreign powers were sharpening their teeth to attack Russia. The Anti-Maidan movement would ensure that they could not do so, with violence if necessary…
Nemtsov frequently appeared on lists of “traitors” published online by extremist groups, and given that many radical Russian nationalists have been fighting a war in east Ukraine for the past six months, there have long been fears that the bloodshed could at some point move to the streets of Moscow.

As The Economist noted, Nemtsov wrote this a year ago:

”National traitors”, “fifth column”, “fascist junta”—all these terms are coming from the same Kremlin office…The Kremlin is cultivating and rewarding the lowest instincts in people, provoking hatred and fighting. People are set off against each other. This hell can not end peacefully.

Walker:

… If, as [Putin spokesman] Peskov says, it was senseless for the Kremlin to kill someone who posed very little threat, that leaves another option that is perhaps even more terrifying: that the campaign of hate that has erupted over the past year is spiralling out of the control of those who manufactured it.
“Actually it would be in some way less worrying if Putin had ordered Nemtsov’s killing,” wrote Ksenia Sobchak, a socialite turned journalist and opposition activist [and daughter of the St. Petersburg mayor, who was, in some senses, Putin’s first political sponsor]. “It would be an awful system, but at least a system, a manageable system. But I feel, unfortunately, this is not the case. There is no Putin who gave a command to kill. But there is a Putin who has built an appalling terminator, and he has lost control of it.”

Mark Galeotti admits that he has “no idea” who actually gave the order to kill Nemtsov, but leans towards the view that he was gunned down “by murderous mavericks”:

The reason they felt obliged to go and gun down a frankly past-his-peak anti-government figure is highly likely to be …the increasingly toxic political climate that clearly is a product of Kremlin agency, in which people like Nemtsov are portrayed as Russophobic minions of the West, enemies of Russia’s people, culture, values and interests.

Of course, the Kremlin would have anticipated that a hit like this would have produced this type of (in some senses exculpatory) speculation, further clouding what was always bound to be a usefully confused picture.

Regardless of who may or may not have given the order to kill, I find it hard to disagree with Galeotti’s broader conclusion:

I do not believe Putin is intent on World War III, or wants to create a neo-Stalinist terror-state, or do any of the other things the more extreme critics aver. But I suspect that in the name of holding onto power (his greatest ambition) and asserting the true sovereignty of Russia (his second greatest), regardless of the opposition of liberals at home, Ukraine, the West, or whoever, Putin has taken a step too far along a dark and dangerous path for him ever to be able to step back or even, worst yet, stop walking forward…