An investigation into a massive fire at an illegal timber dump has been closed because of insufficient evidence.
The blaze at Manor Farm, near the A10, was still smouldering nine months later.
An investigation was launched after the fire was brought under control.
West Norfolk council, which co-ordinated authorities involved in the aftermath, said: 'Norfolk fire service has investigated the cause of the fire. They were unable to identify the exact cause of the fire, or who started it, due to the lack of any evidence.
'The outcome is that the most likely cause was deliberate action by person or persons unknown.
'Norfolk police have concluded their investigation. Following the report provided by the Norfolk fire service the police investigation has been closed due to insufficient evidence to pursue. If further information comes to light this may be reviewed further.'
The council said tests have been carried around the site of the fire by environmental health officers.
It added: 'We have completed a contaminated land report which concluded that while there are sources of contamination on-site, the contaminants are not at high enough levels to pose a significant risk to off-site residents, the environment or nearby water courses.'
Mark Fuller, who owns the site, has now agreed to allow Norfolk County Council to remove other waste which has been illegally-stored on the site and sell it on.
An investigation is also under way into a major fire which broke out in a scrap yard at Bawsey, near King's Lynn, on Monday night.
Six appliances and a water carrier were needed to bring the blaze under control.
Firefighters are now using a construction grabber to dismantle the pile of household waste and submerge it in water. They say the smouldering waste pile contains around 1,000 tonnes of material and expect the job to take three days.
People living around the site have been advised to keep their windows closed and contact their GP if they have health concerns.
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