Detectives and forensic teams have scoured the site of a recycling plant destroyed in an arson attack to hunt for clues that could lead them to the culprits.

CCTV footage has been seized from businesses near AWM Recycling Ltd in Western Way in Moxley. Police are studying hours of footage to see if they captured the suspects on film. Officers revealed yesterday they are hunting for four people seen around the site shortly before the huge blaze broke out at 4am on Wednesday.

Two people in dark clothing were seen acting suspiciously at the rear of the building, while a man and a woman were also spotted close to the scene.

Fire investigation teams joined police at the site yesterday to search through the wreckage left after the ferocious blaze. A door at the rear of the property showed signs of forced entry.

At its height, around 100 firefighters tackled the blaze. Eighty residents were evacuated and health warnings issued amid asbestos fears as clouds of smoke billowed into the sky.

Det Insp Gary Plant said: “Our investigations are now complete at the premises. The building has now been handed back to the landlord.

“Our investigation is continuing. There is CCTV footage and we are currently looking at it to see if it has revealed any clues.

“We are looking for two people wearing dark clothing who were acting suspiciously at the rear of the property just before the fire started. A door was found to be insecure at the back of the property. The premises has been treated as a crime scene.”

West Midlands Fire Service spokesman Jeremy Sharpe said: “The final pockets of fire have been extinguished and the damping down has been completed. Fire crews have now left the premises. We have been assisting the police in their investigation.”

Families were forced to flee their homes when the fire caused acrid black smoke to pour into the sky. There was health fears due to asbestos in the roof of the building and fears about asbestos which was being stored in skips on the site.

The Environment Agency has also used powers under the Police and Criminal Evidence Act to enter the site. The nature of the investigation is not known.