McDonald v. State
In McDonald v. State, 947 A.2d 1073 (Del. 2008), an officer stopped a car for failing to activate a turn signal when exiting a parking lot. Id. at 1075.
Based on events following the traffic stop, the defendant was arrested. Id. at 1075-76.
After the arrest, the officer obtained an arrest warrant for the defendant, based on the officer's sworn affidavit as to events occurring before and after the traffic stop. Id.
At the suppression hearing, the defendant argued that the officer could not have had probable cause to believe a crime was committed since Delaware's motor vehicle laws did not require a driver to signal when entering a public highway from private property. Id. at 1076-77.
The officer testified at the suppression hearing, articulating additional factors justifying his traffic stop of the car that had not been included in his sworn affidavit. Id. at 1078.
The McDonald Court held that the "four corners rule" prevented the trial court from considering factors not identified by a police officer in an affidavit of probable cause to arrest when determining whether that officer had probable cause to conduct a traffic stop preceding the arrest, noting that the officer's "sworn affidavit . . . executed in support of the . . . warrant has determinative probative value because it is the only contemporaneous evidence of why he stopped the motor vehicle several hours earlier that day." Id. at 1078.