That New England Patriots owner Robert Kraft pleaded innocent to two counts of soliciting prostitution in connection with the recent massage parlor sex busts seemed curious at first.

He's claiming he didn't do it? When there's supposedly video and everything?

And indeed, investigators say they have images of Kraft, 77, engaged in sex acts with spa workers.

The question is whether they'll get to use that evidence at trial. And if they don't, Kraft and other alleged "johns" could skate.

More: Alleged Florida sex spas: The whole story

More: Accused 'johns' may need to attend class on human trafficking

Kraft's attorneys, along with the lawyers representing several accused "johns," are challenging the way law enforcement got those allegedly incriminating images.

It's called a "sneak and peek" warrant; law enforcement convinces a judge that the crime being committed is so egregious that authorities must be allowed to access private property without the knowledge of those under investigation.

At the Orchids of Asia Day Spa in Jupiter, where Kraft is accused of receiving sexual favors, law enforcement used a "fake bomb threat" to get inside the business and plant hidden cameras, according to court filings. This jibed with a Feb. 22 New York Times story, where the owner of another business in the same strip mall said a "swarm" of police vehicles pulled up and evacuated the massage parlor on Jan. 18, claiming a suspicious package or bomb threat; but no other business in the mall was evacuated.

"Sneak and peek" warrants were made legal by the Patriot Act, passed after the 9/11 attacks. The idea was to target terrorists, but they're almost never used for that purpose: in 2013, for example, 11,000 such warrants were issued — and only 50 were related to terrorism, while 9,401 were part of a drug investigation.

The key constitutional question for judges in the sex spa cases will be whether the allegations here were sufficient to justify the use of this type of warrant.

On the surface the answer might appear to be: of course. After all, sex trafficking is a heinous crime.

But no charges of sex trafficking have actually been filed in the case involving the Jupiter spa. Indeed, though 10 Florida spas were allegedly involved in the alleged trafficking ring, only one charge of trafficking has actually been filed, in Indian River County.

As Martin County Sheriff William Snyder has argued, that doesn't necessarily mean it wasn't happening; trafficking is a hard crime to prove and requires victims who are willing to cooperate.

But if, ultimately, authorities can't make additional trafficking charges stick — or even bring them — it bolsters the argument made by Kraft's attorneys that the argument for the warrant was "founded on a fiction," that the supposed signs that sex trafficking was happening inside the spa were anything but definitive.

Legal experts say "sneak and peek" warrants are pretty rare. Celeste Higgins, a University of Miami law professor, told the South Florida Sun-Sentinel she'd never seen one during her 25 years as a federal public defender. And when they're used "for a common crime — quite frankly, as insignificant as basic prostitution — it’s very, very troubling,” she said. “That means there is no limit when they could use” it.

Kraft's attorneys argue the warrants were "constitutionally problematic." Prior federal cases utilizing the warrants "involved felonies that were far more serious than the misdemeanor prostitution alleged to have taken place here, and the justification for the invasion was far stronger."

Not all legal experts agree; Jonathan Witmer-Rich, a professor at Cleveland State University's Cleveland-Marshall College of Law and a former federal public defender, told the Sun-Sentinel human trafficking cases are serious; and "from that perspective, it does seem like an important enough investigation to use this tool."

But the key question will be: What do the judges in these cases think?

Kraft and the other alleged "johns," after all, face only misdemeanor prostitution charges. To use this type of warrant to snare them amounts to using a sledgehammer to smash a housefly.

If the judge agrees, and tosses the video evidence, the case against these supposed "johns" could fall apart.

That, coupled with the dearth of actual trafficking charges, could turn this high-profile bust into a bit of a bust. That would be a shame if in fact trafficking was occurring here.