In particular, investigators would like to hear from the rider of an off-road motorcycle heard in the area around an hour prior to the blaze, which occurred at 9.15pm.

A police arson chemist deemed the fire Pembroke Secondary College as suspicious this morning.

The fire was the fourth at a Victorian school in three weeks.

CFA spokesman George Ellis said up to three classrooms were damaged, but the wing most affected was predominately empty because it is being demolished.
A combination of CFA and MFB firefighters were able to bring the fire under control by about 10.15pm.
"There was nothing in the classrooms. That's why it didn't take long to bring it under control,'' he said.
CFA captain Tony King said asbestos was believed to have been in the building, but that 80 per cent had been removed ahead of demolition.
Police guarded the crime scene overnight and will continue to keep watch until an arson chemist examines it this morning.

Mr Ellis said fire investigators would also return to the scene to determine the cause of the blaze.
The fire follows a pledge by the State Government to provide a security service to monitor schools after four school fires in recent months were found to be deliberately lit.
In the past three weeks, Ashwood College, Seaford Park primary and Berwick's Kambrya College have all been struck by fires.