The Iranian regime’s potent espionage and assassination network in Europe has operated largely without interruption since the Islamic revolution of 1979. European governments have caught and imprisoned individual terrorists, yet they fail to deter Tehran because they only punish the perpetrators, not the regime that gives them their orders.

German prosecutors have filed charges of conspiracy to commit murder against Assadollah Assadi, an Iranian diplomat connected to Tehran’s Ministry of Intelligence. Assadi recruited agents to bomb a conference in Paris, but police apprehended them before the attack. The question now is whether European governments will hold Tehran accountable in ways that signal zero tolerance for state-sponsored terrorism. So far, no European government has cut diplomatic ties or halted business contracts.

Assadi apparently recruited a Belgian couple with Iranian roots to plant explosives at a 25,000-person gathering in Paris organized by an exiled Iranian opposition group. Belgian police found the couple with 500g of TATP explosive and a detonator.

Speakers at the Paris conference included former New York City Mayor Rudolph Giuliani and former House Speaker Newt Gingrich.

The seriousness of the allegations prompted the Austrian government, to whom Assadi is accredited, to demand that Iran’s ambassador to Vienna “lift the immunity of the Iranian diplomat.” Soon after, the Netherlands announced that it had expelled two Iranian diplomats for undisclosed reasons.

Such pinpricks are unlikely to influence Iran’s calculus when it considers whether to order the next attack. In contrast, if European governments threatened to impose sanctions at a time when the Iranian economy is deeply vulnerable, Tehran might have to rethink its strategy.

While the failed Paris attack is one of the most brazen examples of Iranian crime and terrorism on the continent in recent years, European governments have reported on many illicit activities. In October 2017, the Dutch ministers of defense, foreign affairs and foreign trade sent a letter to the country’s parliament stating that “Dutch technology was used in programs of mass destruction and means of delivery in Iran, Pakistan or Syria.”

In March 2017, a Berlin court sentenced Haidar Syed-Naqfi, a Pakistani citizen, to four years in prison for spying on behalf of Iran’s intelligence agency “against Germany and another NATO member.” Syed-Naqfi’s actions, according to German authorities, were a “clear indication of an assassination attempt.”

Before his arrest, Syed-Naqfi spied on the French-Israeli business professor David Rouach and conducted surveillance of pro-Israel and Jewish organizations in Germany.

The past year’s espionage and assassination attempts mirror those of the last decade. Between 2007 and 2017, according to a German government report, authorities conducted criminal investigations of 22 cases of alleged Iranian espionage. During the same period, Russia’s spy activity involved 27 investigations.

One of the deadliest Iranian attacks in Germany illustrates how Tehran escapes accountability. In 1992, the Iranian government ordered the execution of Kurdish dissidents at the Mykonos Greek restaurant in Berlin. A German court ruled that the regime was responsible for the killing of three Iranian-Kurdish leaders and their translator. Judge Frithjof Kubsch declared at the trial’s conclusion: “The Iranian political leadership ordered this crime,” adding, “They made a decision to silence an uncomfortable voice. This is an official liquidation measure ordered without a verdict.”

Berlin’s prosecutor pinned the blame squarely on the shoulders of then-Iranian president Ali Akbar Hashemi Rafsanjani and Supreme Leader Ali Khamenei. Between 1979 and 1994, Iran, according to the CIA, reportedly attempted to assassinate over 60 individuals in Europe, including several in Germany. Nonetheless, Germany merely recalled its ambassador for consultation and expelled four Iranian diplomats. Iran reciprocated with the same diplomatic measure.

Chancellor Angela Merkel released the Mykonos killers in 2007, even though they received sentences of life in prison. Upon returning home, Iranian perpetrator Kazem Darabi was greeted by senior Foreign Ministry officials. The regime bestowed a Mercedes and a cash award to another perpetrator who fled before he was caught. At the time, many European countries cut diplomatic ties with Iran, only to have re-established them months later. And Germany does not seem to have pursued its international warrant that still exists for then-Minister of Intelligence Ali Fallahian for ordering the attack.

After the most recent plot to bomb the conference in France, one official commented that “if Iran can plot bomb attacks in Paris, they can plot attacks anywhere in the world.” In fact, Iran does just that, too often with impunity.

Austria has engaged in similar appeasement of Tehran. In 1989, suspected Iranian agents in Vienna assassinated Kurdish-Iranian leader Abdul Rahman Ghassemlou. While there was a clear trail that led to Iran’s embassy, Austria released the alleged assassin, who carried out the murder which came on the heels of an arms deal with Iran.

With the new Iranian bomb plot in Europe, the alpine state surrendered its best opportunity to send a message to Tehran. Just three days after Assadi’s arrest, Austria’s leaders welcomed Iranian President Hasan Rouhani to Vienna. Rather than canceling his visit, they provided a military honor guard.

Moreover, Austria’s chamber of commerce delivered a platform for Rouhani to increase business ties between the two countries.

If nothing changes, Iran will carry out more assassinations on European soil. Instead, the latest Iranian bomb plot should jolt Europe into bridging its differences with the U.S. and mounting a comprehensive international pressure campaign that compels Iran to shut down its terrorism, spy and assassination network.

Benjamin Weinthal reports on human rights in the Middle East and is a fellow at the Foundation for Defense of Democracies. Follow him on Twitter @BenWeinthal.

Toby Dershowitz is senior vice president for government relations and strategy at the Foundation for Defense of Democracies. Follower her on Twitter @TobyDersh.

Follow the Foundation for Defense of Democracies on Twitter @FDD. FDD is a Washington-based nonpartisan research institute focusing on national security and foreign policy.