The British government on Wednesday formally identified two suspects it believes are responsible for the March 2018 assassination attempt on Sergei Skripal and his daughter, Yulia, in the rural English town of Salisbury. That attack left the Skripals in critical condition and a police officer seriously ill.

Here's how the U.K. authorities have identified the suspects and their service as officers of Russia's GRU intelligence service.

As British authorities confirmed today and I noted just following the attack, the Russian strike team utilized an atomizer-based delivery weapon to spray the door handle of Sergei Skripal's residence with a Novichok-class nerve agent. That high-concentration agent was disguised in a false perfume bottle in order to get through British customs without detection. The suspects then discarded the bottle before returning to London from Salisbury. An innocent woman was later killed when she sprayed the bottle's Novichok, what she thought was perfume, on her wrists. Those responsible (named as Ruslan Boshirov and Alexander Petrov) are extremely likely to have been traveling on false identity papers.

But the British government's main basis for identifying the two suspects was cross-referencing port of entry video data at Gatwick airport (where the suspects arrived) with video recordings taken from the area surrounding the Skripals residence in Salisbury. As an indicator of the Russians' lack of concern about eventual detection, they traveled directly from Moscow on an Aeroflot flight (heavily utilized by Russian intelligence services) rather than from another nation on fake third nation passports. That enabled British authorities to quickly identify the two suspects.

The next step was establishing the two individuals' link to the GRU intelligence service. This assessment was attained from a range of signal, human, and technical intelligence material (some historic) drawing specific connection to the GRU itself. Yet it is now clear that the GRU wanted the U.K. to know that its officers were responsible for the attack. By using two active operations officers rather than " cutouts" (deniable assassins without obvious links to the GRU) President Vladimir Putin aimed to have his officers identified. In turn, he hoped to achieve the strategic effect of threatening declared traitors in disdain for Western warnings against such threats. It is no coincidence GRU officers were assigned to kill Skripal — the former Russian intelligence officer turned British agent is a former GRU officer himself.

There is one final factor here. Under the direction of Russian defense minister and Putin wannabe Sergey Shoygu, the GRU has grown increasingly aggressive in recent years. These efforts are strongly believed to have involved GRU assassinations of officials believed to be traitors and of journalists who ask too many questions about GRU cutouts. GRU chief Igor Korobov is a longstanding GRU officer who is well-liked by Putin for his loyalty and penchant for high-risk operations. Indeed, Putin awarded Korobov a hero of the Russian federation medal in 2017 for his success in cyberoperations targeting the U.S. 2016 presidential election.

But we shouldn't sit idle here. The West should respond to this outrage with new sanctions and the more aggressive confrontation of Russian intelligence operations.