POLICE are hunting for a highly organised gang who masterminded a second cable theft from a busy railway line, again forcing part of it to be shut down.

A section of the Aberdeen to Inverness line was yesterday closed for the second time in three days, causing disruption to thousands of passengers.

One-quarter of a mile of cable was stolen in the early hours yesterday, close to where a mile of cable was removed near Huntly at the weekend.

Police are keeping an open mind as to whether the same gang is responsible but they say both thefts were carried out by a gang who knew what they were doing as the copper cable, which powers the line's signalling system, was live at the time and could easily have killed or injured them.

The gang also needed a method of winding in the heavy cable once they cut it down from telegraph-style poles which carry it, and suitable vehicles for transporting it away.

Network Rail knows exactly when the power was cut because a signal box was manned and engineers were nearby still testing the system after Sunday's theft.

Police have now brought in a helicopter to help scour the area for suspicious activity and are also questioning scrap merchants.

A Network Rail spokesman said: "This was not an opportunistic crime. Nine times out of 10, cable theft is committed by organised gangs. You have to know what you are doing. In the past we have had some end up minus a hand or dead, because there are thousands of volts running through the cables."

He said the gang cut the power but would not reveal how this was done.

"The signalman in the box noticed that there was no power to the signals at a nearby level crossing, so raised the alarm quickly. The British Transport Police (BTP) were alerted at 1.40am. As soon as the power was cut the whole system went to red," he said.

The second incident took place close to Leith Hall, in Kennethmont, at a place where the rail line is beside the B9002. It is about one mile from where Sunday afternoon's theft took place,

Chief Superintendent Ellie Bird, of BTP, said: "This is the second theft in three days from the same area, and officers have stepped up their patrols in the location in order to identify those responsible.

"It is of particular concern that thieves are not aware of the dangers and continue to put their lives at risk by trespassing on the tracks and cutting live signalling cable.

"There is an assumption that cable theft is a victimless crime, with the only effects being felt by the railway industry. As we have seen here, this is simply not the case. A section of the line has been brought to a halt while essential repairs are carried out and these incidents have caused extensive disruption to journeys, with hundreds of trains across the Aberdeenshire area being cancelled."

The section of the track between Inverurie and Huntly was closed until yesterday afternoon.

Ms Bird added: "We have ­officers carrying out a full search of the track to gather any forensic evidence as well as viewing CCTV in and around the surrounding area."

She said that, as part of the investigation, police would also like to hear from anyone who saw any suspicious activity in the Huntly and Kennethmont area over the past few days, or any vehicles which may have been close to the rail line.

"We will have a team of officers visiting scrap metal dealers in the area making it harder for thieves to sell on stolen metal for a measly profit. We will not only be ­stepping up patrols on the ground, we'll also be utilising a helicopter in the area giving us a view for miles to monitor any suspicious activity," she said.