It is received wisdom in the United States government that good law enforcement is good security. As we are seeing once again, it ain’t necessarily so.

On Saturday, the Justice Department announced the arrests of three Muslim men in an ongoing terrorism investigation. (Justice, of course, said “three men” — I’m adding the “Muslim” part that the government prefers to gloss over.) David Kris, DOJ’s national-security chief, called the investigation “fast-paced.” A better choice of word would have been “frenetic,” since the “fast-paced” investigation has failed to produce any actual terrorism charges. The men, reportedly Afghan immigrants, have been charged with making false statements during an interrogation by the FBI.

Obviously, that’s not what the feds are really after here — any more than the feds were really trying to make immigration cases or secure the testimony of material witnesses when, after the 9/11 attacks, they used the immigration laws and the material-witness statute as legal hooks to arrest and hold terrorism suspects.

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It has been apparent for almost 17 years — since the 1993 World Trade Center bombing — that we need an administrative-detention law. Though President Obama has referred to the 1993 WTC investigation as a model, it actually underlined the shortcomings of approaching terrorism as a mere law-enforcement problem. While the FBI raced to stitch together the forensic proof that the explosion was a bombing, that the bombing was a conspiracy, and that the conspiracy was an international terrorist enterprise, major participants in the bombing were permitted to flee — several of them overseas. To the extent those players had been identified (and most of them could not be identified quickly), the FBI had not yet uncovered the evidence needed to arrest them for terrorism.

Under American law, a suspect may not be arrested absent probable cause that he has committed a crime. In the standard investigation — one in which the police have not infiltrated a conspiracy with an informant who can tell them, in real time, who the bad guys are and what they’re up to — police scramble from the moment they get wind of a plot. The reason is simple: With a few details, experienced cops usually know a plot is under way before they can prove a plot is under way. To build a case that will stand up under the burdens imposed by due-process rules, it takes time: sometimes weeks, often months if key evidence is located outside the U.S., and especially if that evidence is composed of communications in Arabic or another foreign tongue, requiring arduous translations accurate enough for use in court.

These are burdens we are happy to bear in standard criminal cases, say, drug trafficking or fraud. They incorporate safeguards that prevent innocent people from being convicted. Yes, it is regrettable that drugs are dealt and fraud victims fleeced while the police are methodically building their case, but these are the consequences we must accept in exchange for a greater good: ensuring that the liberty of Americans who are presumed innocent is not disturbed unless our government has enough proof to justify prosecution.

National security alters the risk calculus. The damage that can be done to life and property by mass-murder attacks is incalculable; if they can be stopped, we must stop them — even if the time is not ripe for arrests based on probable cause.

Still, we pay a prohibitive price when we end an investigation too soon and make arrests too quickly. In a broad conspiracy, the leaders almost always are the most insulated actors. The highest-ranking players resist speaking on the phone and appearing in public, dealing instead with a few trusted aides. Usually, they have little or no contact with the foot soldiers who perform the hands-on commission of crimes — the crimes that first draw police attention. If police start arresting the underlings before they’ve gathered evidence showing the complicity of the higher-ups, the leaders will slip away. In a terrorism case, that means the police fail to capture the most dangerous jihadists: the ones capable of ordering, planning, and recruiting for future mass-murder attacks.

This is the bind we’ve put ourselves in by wedding our security to our criminal-justice processes: Arrest early to prevent an attack and prosecutors won’t be able to make charges stick — certainly not against the most significant terrorists. But if we wait too long in order for law enforcement to build a solid case, we increase the chance of a catastrophic terrorist attack.