Understanding a Franks-Mann Motion in Wisconsin Criminal Law

When law enforcement seeks a search warrant, they must convince a judge there’s probable cause to believe that evidence of a crime will be found at a specific location. That probable cause is usually established through an affidavit — a sworn statement by an officer or investigator.

But what happens when that affidavit includes false statements, omissions, or misleading information?

In Wisconsin, your defense attorney can challenge the truthfulness of a warrant affidavit through what’s known as a Franks-Mann motion — a powerful legal tool that protects your Fourth Amendment rights against unreasonable searches and seizures.

At Johansen Law Office, S.C., we frequently analyze search warrants for these kinds of issues. Below is an overview of what a Franks-Mann motion is, where it comes from, and how it can help your defense.

1. The Origins: Franks v. Delaware (1978)

The foundation for this motion comes from the landmark U.S. Supreme Court case Franks v. Delaware, 438 U.S. 154 (1978). In Franks, the Court held that:

A defendant has the right to challenge the validity of a search warrant if they can make a substantial preliminary showing that the police officer knowingly and intentionally, or with reckless disregard for the truth, included false statements in the affidavit used to obtain the warrant.

If the defendant can make that showing, the court must hold what’s called a Franks hearing. At that hearing, the defense can present evidence to prove the affidavit was false or misleading — and if successful, the warrant can be voided, and any evidence seized may be suppressed.

2. Wisconsin’s Expansion: State v. Mann (1996 WI 4)

Wisconsin built on this principle in State v. Mann, 123 Wis. 2d 375, 367 N.W.2d 209 (1996), often cited together with Franks as the “Franks-Mann motion.”

In Mann, the Wisconsin Supreme Court recognized that false or misleading omissions can be just as damaging as false statements. The court ruled that a defendant is also entitled to a hearing if they can show that:

The affiant (the officer) knowingly, intentionally, or with reckless disregard for the truth omitted material facts that would have undermined probable cause.

In other words, it’s not just what the officer said — it’s also what they left out.

For example:

• Failing to disclose that an informant was unreliable or untested,

• Omitting exculpatory information (e.g., someone else had access to the location),

• Leaving out context that weakens the link between the suspect and the evidence.

  
  

If the omission or falsehood is material — meaning it affects the magistrate’s probable cause determination — then the warrant can be invalidated, and the evidence obtained as a result must be suppressed.

3. The Legal Standard for a Franks-Mann Motion

To successfully obtain a Franks-Mann hearing in Wisconsin, the defense must:

1. Make a substantial preliminary showing that the warrant affidavit contains a false statement or material omission.

2. Show that the falsehood or omission was made knowingly, intentionally, or with reckless disregard for the truth.

3. Demonstrate that the false or omitted information was necessary to the finding of probable cause.

   
   

If those elements are met, the court will hold an evidentiary hearing where the officer may be called to testify under oath. If the court finds the warrant was issued based on false or misleading information, the evidence is suppressed under the exclusionary rule.

4. Why Franks-Mann Motions Matter

Search warrants are a cornerstone of criminal investigations, but they rely on the integrity of the information provided to judges. When that integrity is compromised — whether through exaggeration, selective reporting, or reckless omission — a person’s constitutional rights are at risk.

Franks-Mann motions serve as a critical check on police power, ensuring that citizens are not subjected to unlawful searches based on misleading or false information.

These motions are especially relevant in cases involving:

• Drug searches

• Weapons possession

• Internet or electronic evidence searches

• Domestic or vehicle searches based on informant tips

  
  

5. How Johansen Law Office, S.C. Can Help

At Johansen Law Office, S.C., we carefully review every detail of a search warrant — the affidavit, supporting documents, and police reports — to uncover inaccuracies or omissions that may have influenced the judge’s decision.

Our team has the experience and tenacity to:

• Identify misleading statements or omissions,

• File a Franks-Mann motion on your behalf,

• Cross-examine law enforcement officers at a hearing, and

• Fight to suppress unlawfully obtained evidence.

  
  

If your rights were violated during a search or arrest, we’ll challenge that violation in court and work tirelessly to protect your freedom.

Final Thoughts

The Fourth Amendment protects you from unlawful searches — but those protections only work when they’re enforced. A Franks-Mann motion is one of the most effective ways to ensure that police are held accountable for the truthfulness of their warrant applications.

If you’ve been charged with a crime following a search in Wisconsin, contact Johansen Law Office, S.C. today for a confidential consultation. We’ll review your case, analyze the warrant, and determine whether a Franks-Mann challenge could make a difference in your defense.

Disclaimer

This post is for informational purposes only and does not constitute legal advice. Each case is unique, and you should consult with a qualified attorney for specific legal guidance.