The nerve agent attack on former Russian double-agent Sergei Skripal and his daughter sends a powerful message to the rest of the world: the assassins aren’t playing by the rules.

On March 4th, Skripal and his daughter Yulia were hospitalized after collapsing in Salisbury, England. They had been poisoned with a Novichok nerve agent developed by the Soviet Union during the Cold War. The British government, as well as France, the US, and Germany, have blamed Russia for the attack. Britain’s prime minister Theresa May said that it is “highly likely” that it was either a state-sponsored attack or that Russia let another group — terrorists, for example, or organized crime — acquire a military-grade toxic nerve agent.

“They’ve had plenty of opportunities to kill Skripal.”

Still, if the Russian government really was responsible, why use a nerve agent that could so easily be traced back to them? “They’ve had plenty of opportunities to kill Skripal,” says Michael Kofman, an expert on Russian military affairs at the nonprofit research organization CNA. “And there are, frankly, a myriad of much simpler and more practical ways of doing it.”

But using chemical weapons is about more than just killing. These taboo weapons are instruments of terror, and their use is designed to send a message to the world: that the power behind the attack — Russia, according to the UK — doesn’t think anyone else is ruthless enough to retaliate effectively. And to others who might consider betraying Russia to foreign powers, it’s that snitches get more than stitches — they get murdered.

Of course, it’s possible that using a rare nerve agent was an effort to evade detection, Cindy Vestergaard, director the Stimson Center’s nuclear safeguards program, tells The Verge. But we’ve seen similarly public and brazen attacks before, Vestergaard says. In 2006, Alexander Litvinenko was poisoned with polonium-210-spiked tea. And before that, in 1978, BBC journalist and Bulgarian dissident Georgi Markov was killed when he was poked with a ricin-tipped umbrella on Waterloo Bridge in London.

“It’s a ‘fuck you!’”

The other possibility is that these attacks are intended to send a message — and that message is clear, Vestergaard says: “It’s a ‘fuck you!’” Using Novichok as a calling card could be a way of saying that Russia doesn’t care about looking guilty because whatever retaliation the UK and the West might muster isn’t frightening enough. After all, an in-kind response is off the table, says Michael Kimmage, a professor at The Catholic University of America and expert in Russian foreign affairs. “I don’t think anybody is going to propose that we send James Bond over to kill somebody,” he says.

If only one side is willing to be ruthless, it changes the rules of the game. This “etiquette of espionage,” for example, held that former spies were off limits for assassination attempts, according to a Moscow Times op-ed by Mark Galeotti, a senior research fellow at the Institute of International Relations, Prague. And there’s an international treaty against using chemical weapons, so using them for assassination attempts on foreign soil are beyond the pale. “They do things like this intentionally to show that they in no way will be limited by what are considered to be established rules and norms of behavior,” Kofman says.

“If you betray us, we will kill you.”

That message is also aimed at anyone considering telling Russia’s secrets to foreign powers, Kimmage says. “One very clear message is ‘If you betray us, we will kill you’ to put it into blunt, mafia-like terms,” he says. “‘You won’t be safe anywhere, even if you’re in Britain.’” The attempted murder of Sergei Skripal made an example out of him, and the theatrical method ensured that the press picked up the message and distributed it around the globe.

There’s a deeper meaning the world should also take away from this latest use of a chemical weapon, Vestergaard writes in an analysis for the Stimson Center: “The threat of chemical weapons not only endures in the 21st century, but is spreading.” In the last few years, the Assad regime unleashed chemical weapons on civilians in Syria; ISIS used mustard gas in Syria and Iraq; state-sponsored assassins used the nerve agent VX to kill Kim Jong-nam, Kim Jong-un’s half-brother. And now, a chemical weapon made for the battlefield was used in a UK cathedral town, in the attempted murder of a UK citizen.

Vestergaard writes: “It seems the chemical peace is not just broken; it is shattered.”