This educational guide is based on the linked primary sources. It is not a Court publication, is not affiliated with the Court, and is not legal advice.
In brief
Overview
Illinois argues that a drug‑detection dog sniff performed during a lawful traffic stop is not a Fourth Amendment search and therefore requires no Fourth Amendment justification.
Background and question before the Court
According to Justice Stevens, Roy I. Caballes was stopped on Interstate 80 for driving 71 mph in a 65‑mph zone.
According to United States (amicus curiae), according to United States (amicus curiae), during the stop, a second officer used a drug‑detection dog to sniff the exterior of Caballes’s vehicle.
According to United States (amicus curiae), according to United States (amicus curiae), the central legal question is whether that dog sniff, performed during a lawful traffic stop, requires a separate Fourth Amendment justification.
What each side argues
Illinois (Petitioner) Position
Illinois maintains that a dog sniff is not a Fourth Amendment search and therefore requires no Fourth Amendment justification.
Roy I. Caballes (Respondent) Position
Source-limited. The record does not yet support a complete account.
What happened at oral argument
Justice Stevens asked whether the officers knew in advance that Caballes was a target and questioned the reasonableness of arresting everyone traveling at 70 mph on I‑80.
According to Justice Scalia, justice Scalia questioned whether any observation by a police officer, such as following a suspect, constitutes a search.
Justice Ginsburg asked whether the presence of a dog in the arresting officer’s car would change the analysis.
The case was submitted after oral argument.
What the Court decided
Why it matters
Terms to know
No glossary terms are available for this guide.
Primary sources
Read the source materials on the official site or open the immutable repository copy used for this guide.
- d4a0d2bc3c4b3942b39b-r1-9bc66f11da07fbab.pdforal argument transcript
Guide generated September 21, 2026. Automated validation accepted this version.