When intel isn’t shared, criminals win

British police were justifiably furious when evidence from their investigation into the Manchester terrorist attack found its way into news reports. The leaks undermine the investigation and the confidence of victims and witnesses, whose cooperation is crucial.

The immediate consequence is that Manchester police have stopped sharing information about their investigation with U.S. officials, who are widely believed to be the source of the leaks. That is bad enough. The more long-term danger is that the leaks in this case will be used to argue against intelligence sharing more broadly. That would be tragic.

This does not mean all information must be shared, or that strict rules shouldn’t be applied to how that information is used. And there will always be tension between the public’s right to know about a threat and law enforcement’s need for discretion while investigating it.

Yet it is inarguable that national security requires international cooperation. Intelligence sharing is vital not just to counterterrorism efforts but also to combat crimes such as sex trafficking.

While there are countless systems in place to govern and control such sharing — from NATO to Europol to many layers of bilateral ties — ultimately, they depend on one thing: trust. Countries share intelligence if they believe it’s in their interests. If the trust goes, the flow of useful information may stop. And the reality is that security services are famously protective of their information. It doesn’t take much for them to clam up.

The only winners from a breakdown in cooperation — whether it’s withholding information or failing to adequately support cooperative ventures — are criminals and terrorists.

Breakdowns will still happen, of course. That is worth bearing in mind as Britain and the United States investigate the latest leak, as they should. And it’s worth keeping in mind during Brexit negotiations as the U.K. recalibrates its relationship with Europol, to which it contributes disproportionately but from which it also gets benefits.

In both cases, national leaders will almost certainly support the principle of cooperation. That was the case with Prime Minister Theresa May and President Donald Trump, who met in Brussels Thursday. It’s what happens a few levels down, however, that will give their words meaning.