In Burnsville last spring, a contractor was sent to a foreclosed house by the bank that held the mortgage. When he got there, he found signs that someone had been living in what was supposed to be a vacant house, so he called police. They found a pot-growing operation.

And not long before that, airport police contacted the Dakota County Drug Task Force after learning that a package headed for a vacant South St. Paul house contained pounds of marijuana. Narcotics officers set up a sting and nabbed a man who had broken into the house earlier that morning as he waited for the delivery. Officers arrested him after he accepted the UPS package and walked away.

Those are among scattered cases of narcotic activity that police say are turning up across the metro in foreclosed homes.

Cmdr. John Grant of the Dakota County Sheriff's Office said the foreclosures that have mushroomed in the past few years have hurt people and neighborhoods in various ways, including criminals in houses that long stand vacant.

"I would like to see neighbors take it upon themselves to report criminal activity," Grant said. "If you know of a house in your neighborhood that is vacant and/or foreclosed, and you see suspicious activity -- strange vehicles, strange people, maybe lights on in the residence, a screen that might be off, or a broken window -- contact law enforcement."

Authorities note that since the foreclosure crisis began in earnest in late 2006, there have been plenty of targets for such criminals. There were, for example, 2,082 foreclosed homes sold at Dakota County sheriff's sales in the past year alone.

"We're seeing a lot with parcel packages," Grant said of narcotics investigations involving vacant homes across the metro. "UPS will receive a package of dope, and the address on there will be a foreclosed property because that's what our suspects are looking for. So they'll have a package delivered to a foreclosed home, and they'll just sit there and wait for it."

Grant said methamphetamine smugglers will get the address of a foreclosed home and call their cohorts in Texas, for example, and give them the address, often using an alias name as the recipient.

"They'll just track that package through the Internet and say 'OK, that package should be here at 123 Main Street Thursday morning at 9 o'clock, and we'll go out there and wait for it,'" Grant said. Sometimes they break in, and sometimes they wait outdoors, he said.

Here and nationwide, authorities are seeing another scenario involving foreclosed homes: Criminals will buy a house for a pot-growing farm and sometimes let it go into foreclosure, said Sgt. Jason Polinksi of the Dakota County Drug Task Force. The pot farmers can make much more selling three or four crops a year than the house is worth, he said.

"I'm sure it happens more often than we know," said Sgt. Joe Leko of the drug task force. "Those are hard to stumble across because you rely on the neighbors and citizens to report something suspicious."

Leko said there have been cases in Apple Valley and beyond where homes have been bought for use as indoor marijuana farms, but nobody lives there. The pot farmers try to fool the neighbors.

Those homes typically have drapes and blinds that are always closed, and perhaps lights that come on at specific times, thanks to a timer, Leko said. Those houses, he added, resemble what homes look like when somebody's on vacation.

Still, there are telltale signs.

Because of the heat and humidity used to grow marijuana, pot farms often have moisture on the windows. Another indicator, Leko said, is that in the winter, pot farm homes have no snow on the roofs.

Officers say the high humidity and heat foster rampant mold growth. Along with the mold and the chemicals used to grow the marijuana, and the spores the plants produce, there's growing health concerns not only for police who bust those operations, but for consumers who might buy the houses later from the banks.

Joy Powell • 952-882-9017