MADISON, Wis. -- Madison police said they are investigating the theft of $7,000 worth of copper and aluminum from a construction site on Madison's East Side.

Police said someone cut the metal from a 1,200-pound rooftop air conditioning unit. The unit was temporarily removed from a building in the 900 block of Williamson Street and left in the parking lot over the weekend.

Police said they are asking local recyclers and scrap metal shops to be on alert.

"We send out a mass e-mail saying, 'We had a thousand pounds of copper taken out of an air conditioner, and if you see someone that comes in with a large amount of copper, would you please get a hold of us,'" said Lt. Mark Brown, of the Madison Police Department.

The project's contractor estimated that the metal weighed several hundred pounds.

Police said this type of crime has gone down in the last few months, because thieves can't resell the copper for much money.