July 26, 2022 – A stop of man who was the only person seen by police in the area where gun shots had been reported by Shotspotter technology was constitutional, the Wisconsin Supreme Court has ruled.
State v. Nimmer, 2022 WI 47 (June 23, 2022), the supreme court held that the stop was supported by reasonable suspicion, in part because police officers arrived at the scene within one minute of receiving the Shotspotter alert and because the officers saw the man digging at his left side with his left hand.
Justice Rebecca Grassl Bradley wrote the lead opinion for a unanimous court. Justice Rebecca Dallet wrote a concurrence, joined by Justice Ann Walsh Bradley and Justice Jill Karofsky joined. Justice Brian Hagedorn also wrote a concurrence.
Two Milwaukee police officers were on patrol one summer night in 2019 when they received a computerized Shotspotter alert in the squad car.
Jeff M. Brown is a legal writer for the State Bar of Wisconsin, Madison. He can be reached by
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According to the alert, four shots had been fired in a residential location about three blocks away. The officers sped to the location without activating the squad car’s siren and flashing lights and arrived there in less than a minute.
When the officers arrived at the location, they saw Avan Nimmer and no one else. Nimmer spotted the squad car and walked away from it, doubling his pace as he did so. One of the officers, Malone, saw Nimmer “digging around his left side with his left hand.”
Pat Down Yields Paydirt
Malone stepped out of the squad car and walked toward Nimmer. As Malone approached Nimmer from behind, he saw Nimmer turn his left side away from him, a move that meant Malone could only make out Nimmer’s right side.
Malone and his partner stopped Nimmer. When Malone began a pat down of Nimmer, Nimmer said “The gun is in my waistband.” Hidden under Nimmer’s shirt on his left side was a .40-caliber Smith & Wesson semi-automatic pistol.
The Milwaukee County District Attorney charged Nimmer with being a felon in possession of a firearm, because Nimmer had previously been convicted of possession with intent to deliver THC.
Circuit Court Denies Motion to Suppress
Nimmer moved to suppress any evidence obtained as a result of the stop.
He argued the stop was not supported by reasonable suspicion and claimed the police had stopped him merely because of his presence in the neighborhood where gunfire had been reported. He could have been just a person out for a walk, Nimmer argued.
The circuit court denied Nimmer’s motion, ruling that the fact police arrived within one minute of the real-time Shotspotter alert was key. Nimmer appealed, and the Wisconsin Court of Appeals reversed the circuit court.
Circumstances Make Stop Constitutional
Justice R.G. Bradley began the lead opinion by explaining that Shotspotter is a system that uses acoustic sensors to identify gunshots. The system is manned by people who listen to the recordings with sensors to distinguish gunshots from other sounds.
At Nimmer’s trial, Malone – a nine-year police veteran – testified that in his experience, Shotspotter was “pretty accurate,” and Nimmer did not dispute the system’s reliability.
Next, R.G. Bradley explained that the U.S. Supreme Court has held that a brief investigative stop is constitutional without a warrant as long as, looking at the totality of the circumstances, it is based upon reasonable suspicion that the person stopped is involved in some criminal activity.
R.G. Bradley pointed out that 1) the Wisconsin Supreme Court has held that the reasonable suspicion test is a “low bar” to surmount, and 2) the U.S. Supreme Court has held that meeting the reasonable suspicion standard requires a lesser showing than the preponderance of evidence standard.
Justice R.G. Bradley concluded that the circumstances in Nimmer’s case required a finding that the police stop was constitutional:
ShotSpotter issues reliable gunfire alerts in real time;
the officers arrived at the location specified in the alert within one minute of receiving the alert;
Nimmer was in nearly the exact location specified in the alert;
the officers saw Nimmer and no one else in that location; and
when Nimmer saw the officers, he made furtive movements.
Justice R.G. Bradley also noted that under federal caselaw, exigency can sometimes supplement the reliability of an informant’s tip and support a finding of reasonable suspicion, and that in Nimmer’s case, the police officers were investigating a shooting in a residential neighborhood.
Dallet Concurrence: ‘This is Not a Trivial Issue’
Justice Dallet began her concurrence by explaining that she was worried that lower courts would construe the lead opinion too broadly.
The majority, Dallet argued, placed too much weight on the fact that the police officers found Nimmer in the residential location specified in the Shotspotter alert.
“Nimmer’s case is unlike many of those cited by the majority/lead opinion, where courts held that the police had reasonable suspicion to stop the only people they found at the scene of reported gunfire late at night, in an alleyway or dead-end street where shots were heard recently, or both,” Justice Dallet wrote.
The majority also placed too much emphasis on the officer’s reliance on the Shotspotter system, Dallet argued, because the system had limits.
“All a Shotspotter report tells the police is that shots may have been fired near a particular place; it doesn’t provide reasonable suspicion that any particular person fired them,” Justice Dallet wrote.
Dallet also argued that the time that elapsed between the fired shots and the police alert was more important than the time it took the officers to respond to the alert.
“This is not a trivial issue; it may be the difference between whether or not an officer’s suspicion of a person on the scene is particularized and reasonable,” Justice Dallet wrote.
‘Cloud of Obfuscation’
Justice R.G. Bradley wrote that Justice Dallet’s concurrence “mischaracterizes the court’s opinion and the precedent it applies, creating a cloud of obfuscation over the opinion so that it will be read to mean something it doesn’t’ actually say.”
R.G. Bradley argued that Dallet’s concurrence relied upon a “straw man” argument – namely, that the majority had sanctioned using Shotspotter “‘as a dragnet to justify warrantless searches of everyone the police find near a recently reported gunshot.’”
That wasn’t the case, Justice R.G. Bradley argued, because the lead opinion’s holding was based on the fact that police arrived within one minute of receiving the Shotspotter alert and found only one person – Nimmer – in that location, facts that would not always be true of police stops made in response to Shotspotter alerts.
In his concurrence, Justice Hagedorn explained that while he agreed that the officers had reasonable suspicion to stop Nimmer, parts of the lead opinion went too far.
In particular, he argued, the issue of whether the “quantum of suspicion necessary to conduct an investigatory stop is lower for the type of … investigation that occurred here” had not been developed enough for him to have an opinion of it.
Consequently, Justice Hagedorn argued, resolving that issue was necessary to dispose of the appeal.