AIRPORT security staff are thought to have raised the alarm after a fire gutted a Derby house.
Firefighters from three different stations spent more than two hours tackling the flames after being called to the derelict bungalow, in Swarkestone Road, Chellaston, at 4.25am on Saturday morning.
The road was blocked to traffic for a number of hours from its junction with Greenwood Road to the Bonnie Prince Charlie roundabout and motorists were advised to use alternative routes in and out of the city.
Following the investigation, a police spokesman said: "The fire is being treated as suspicious and the cause is believed to be arson."
One next-door neighbour, who asked not to be named, said she believes security staff on their way home from a night shift at East Midlands Airport, raised the alarm.
She said: "They were driving past and saw the fire and called 999.
"I was also told they stopped the vehicle they were in to knock on doors and wake neighbours.
"I was woken by a neighbour who phoned me to alert me to say next door was on fire.
"Firefighters used one of their hoses to spray water on to my home and keep the flames away.
"They were brilliant."
Alan Radford, who lives on the other side of the derelict building where the fire took place, said: "We were asleep in bed when there was a knock at the door.
"I went downstairs and, when I answered the door, there was a policewoman there.
"She said: 'Next door's house is on fire, can you move your car please?'
"It was quite a shock.
"The firefighters used a hose to spray water on to our home while others tackled the fire next door. They did a great job."
Mr Radford said the burnt-out bungalow has been empty for a long time and that a planning application has been approved to build homes on land behind it.
On Saturday morning, a police forensics van - as well as one fire engine - were at the scene, while a police officer was directing traffic at the junction of Greenwood Road.
Another near neighbour in Swarkestone Road, who did not wish to be named, said: "My brother lives near to the house so I was concerned that it might have been his house.
"There was lots of water running down Swarkestone Road from the firefighters' pumps.
"The bungalow has been empty for years, it is a proposed entrance for a new housing development."
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