A 15-year-old boy was arrested in connection with an arson attack on a police car in Daventry.
The response team car was parked in Trafalgar Way in Southbrook when it was targeted while an officer attended an incident.
The car, which is in constant use by the police, had its rear windshield smashed and was set on fire.
The boy has been released under investigation pending further inquiries.
Daventry Neighbourhood Sergeant Sam Dobbs said the attack was "stupid, senseless, mindless, reckless criminality which hampers emergency responders".