Police have interviewed a suspect for the arson attack on the Lyttelton Police Station on Tuesday morning.
Lyttelton-based Sergeant Gary Manch said yesterday the enquiry was progressing and CCTV footage was still being reviewed.
The attack at the police station resulted in a police car being seriously damaged and another suffering heat damage.
The Fire Service was called to the station at 2.10 am after a neighbour reported hearing an explosion and seeing flames at the station.
"We're fortunate that the damage wasn't more severe but it was still a blow," he said.
Sergeant Manch said police were waiting for forensic results.