Sometimes M&P Asphalt Paving goes by the name M&F Paving. On occasion, it's M&D Asphalt. But Montgomery County police call it something else altogether: a driveway paving scam.

This year, police say, at least two residents in the Brookeville and Olney communities have been duped by the company, which claims "30 years of experience" and a Laurel address that turns out to be false. Police say such scams occur every year, and they expect the number of complaints to rise along with the temperature.

Criminologists, police officers and analysts have long believed that there is a connection between weather and crime. With the official start of summer this week -- as doors fling open and people head outside -- police expect an increase in overall crime, especially a spike in certain types of offenses.

Skip Baylor, director of crime analysis for Montgomery police, typically sees more "garage-type larcenies" this time of year. As parents do more yardwork and kids ride bikes under the warm sun, they often keep garage doors open and front doors unlocked. This leaves homes vulnerable to outright theft or theft by distraction -- such as when a criminal approaches someone mowing a lawn and strikes up a conversation, while a partner in crime steals an item from the garage or home, he said.

In warmer months, the county also experiences more crimes committed by "transient criminals," Baylor said.

"They'll come into an area. They'll offer services like driveway paving or handy work around the house, often using this as a ruse to do substandard work or take advantage of the elderly or other people who can't take care of themselves," Baylor said.

M&P Asphalt Paving put up fliers offering, among other things, a "special deal for senior citizens." Police said they received complaints about the company starting work on driveways without formal consent, doing an unsatisfactory job and then charging an inflated price. County police say legitimate paving companies do not solicit work door-to-door and will not work without consent.

Crime statistics in the Washington region tend to support the theory that seasons influence criminal behavior, police say. In 2003 and 2004 in Alexandria, for example, crime went down in January, February and March and increased in May, June and July. In one week in April, when the average temperature was 60 degrees, 138 crimes were reported, police said. The next week, when the temperature rose to 74, the number of crimes jumped to 196. A similar effect occurred in October that year.

Statewide in Virginia, serious crimes -- from fraud to homicide to kidnapping -- reached a low of about 31,000 in February 2004 and a high of about 39,500 in July. Some crimes, including larceny and motor vehicle theft, showed a greater relationship to season than did homicide or rape.

There are numerous theories why overall crime increases in the summer, but researchers generally cite two. The first is that during warmer months, people engage in more activities that are not routine or obligatory. They venture outside more often, by vacationing, shopping or doing yardwork. They are not confined to routine activities such as working in an office. So as more people go outside, the chance of a crime or accident happening also increases.

"It doesn't mean that it's more unsafe when you're out and about. It's just that there's more people," said John R. Hipp, a researcher at Odum Institute for Research in Social Science at the University of North Carolina.

According to another theory, warm weather agitates individuals, causing them to be more violent. Although several psychological and sociological researchers have studied this phenomenon, some have disputed its role in crime.

There is less research on whether crime is influenced by short-term changes in weather over a few hours or days, or by precipitation.

"Rainfall is a cop's best friend" is a familiar aphorism, said Ellen G. Cohn, an associate professor of criminology at Florida International University, though its truth is somewhat in doubt.

Cohn has researched more short-term effects of weather on crime. She found that, even in a 24-hour period, crime increased with temperature -- at least to a point. When it gets too hot, "the need to flee the heat becomes more imperative than the need to commit a crime," she said.

There are other explanations for fluctuations in crime, including the school cycle and holidays.

In December, property crimes tend to go up, at least in the weeks before the holidays. During this time, shopping increases, so people leave items visible in cars, and stores put more items out on display, hoping they will sell.

On Christmas Day, however, crime is often low.

"Most criminals do not do crime 24-7. They do have a life outside crime," Cohn said.