Detectives last night stepped up the hunt for an arsonist who struck twice in Huddersfield.
Police and forensic experts continued work at the sites of the mill fires in Slaithwaite and Linthwaite.
And they confirmed both fires were being treated as suspicious.
The first blaze ripped through Colne Mills in Slaithwaite – earmarked for a new supermarket by top retailer Aldi.
At its height, more than 50 firefighters fought the blaze.
Hours later crews were called to the former Hoyle Ing Dyeworks in Linthwaite where another blaze was discovered.
A West Yorkshire Police spokesman said: “Both incidents are being treated as suspicious and we are investigating links between the two fires.
“We would urge anyone with information to get in touch".
Any witnesses should contact Det Con Ian Carruthers via 101 or Crimestoppers on 0800 555 111.”
The blaze at Slaithwaite was one of the biggest for years in the area.
It raged through the mill off Britannia Road, with flames shooting through the roof and windows and a huge pall of smoke drifting across the village.
Hours after the blaze was out, Building Control officers from Kirklees Council were out assessing the damage.
A Kirklees Council spokesman said: “We responded to a request from the emergency services to attend a site on Britannia Road in Slaithwaite to give advice on the structural integrity of a building.
“We are in on-going discussions with partner agencies to ensure that the site and the buildings are safe and secure.”
Linthwaite scrap dealer, Mark Schofield, was drinking in the Wine Bar in the centre of Slaithwaite with friends and colleagues when they saw smoke begin to billow out of the derelict mill.
He said police had arrived immediately – a video van and patrol car were in the village.
But he said it had taken more than 20 minutes for the first fire engine to arrive, despite the village boasting a retained fire station just yards away.
He said: “We just stood there and watched the fire get bigger and bigger.
“The fire was burning away for about 20 minutes and the police had cordoned pretty much the whole of Slaithwaite off.
“They tried to evacuate our bar. I’ve never seen so many vehicles with chequered markings on in one place.
“There was a massive long row of them. Kids have been playing about in that mill trying to light fires for a long time.”
Brian Walker, a semi-retired man and amateur wood carver of Olney Street, Slaithwaite, said: “The fire drew quite a crowd, you could hardly miss it. It was a warm evening and everyone was out in the pubs.”
Darren Eastwood, who runs The Hardware Company, just yards away, said: “There was a police officer with her back to the fire when her colleague in a car shouted to her: ‘There’s a fire!’
“There’s been a lot of problems with vandalism and I caught someone breaking in once. I think this fire was inevitable really.”
Caryl Middleton, who runs a shop nearby, said: “I could see the blaze from our house in Nabs Lane, the smoke was really thick and black. My husband came down to see whether our shop was OK.”
Gordon Cox, of Banks Road, said: “This has been waiting to happen. Kids have got in and broken almost every window over the years.
“I was at home about a quarter-of-a-mile away and you could see the smoke.”
Fire crews from several stations in both Huddersfield and Halifax were called to tackle the blaze and had the fire under control within three hours.
They remained at the scene well into the early hours damping down.
At one point, the crews had five large jets in use and also deployed an aerial appliance from the opposite side of the Huddersfield Narrow Canal, which runs alongside the complex.
The crews were called out to the second incident at Hoyle Ing shortly after 5am yesterday.
The fire was in one section of the range of buildings and was quickly tackled.
Police remained at the scene throughout much of yesterday carrying out inquiries.