PCSOs saw a man trying to get into parked vehicles.
The police community support officers were in a marked police car in Thurland Street, in Nottingham city centre, where an assault had been reported.
As they kept an eye on the scene, they spotted a man trying the door handle of a parked car.
The same man then climbed up a parked lorry, hooked his fingers around the top of a window that was slightly open and tried to force it down.
The two PCSOs jumped out of the police car and detained the man. They called for back-up and two PCs swiftly arrived to arrest him on suspicion of vehicle interference.
The 39-year-old was taken into custody for questioning. He has since been released under investigation.
Sergeant Graham Whitt, of the city centre neighbourhood policing team, said: “The two PCSOs had been sent to the location to preserve a scene and in the process they spotted another suspected crime taking place.
“They did an excellent job in detaining the man at the scene so that he could be arrested.
“We continue to deploy high visibility and plain clothes patrols in the city centre in order to deter or catch offenders ‘red-handed’ as we relentlessly target those suspected of wrongdoing.”