A man walked into a high-end jewelry store in the Tysons Corner mall and said he wanted to buy a $10,000 watch. But he was acting kind of strange and looking nervous, police said.

A suspicious salesperson stalled the man, got his name and ran a quick search on him. His name popped up on Prince George’s County’s most-wanted list.

The clerk called police. The man ran away. After a short chase, officers arrested Paul A. Danzo, 41, of Laurel.

That was several days before Thanksgiving. In the days since Black Friday, Fairfax County police have arrested 20 people for retail crimes in Tysons Corner’s retail centers.

“Our officers do an excellent job in training store clerks of what to be suspicious of,” said Fairfax police Lt. Tony Matos, who is in charge of a retail anti-theft team. “That training paid off.”

When police searched Danzo and his car, they found $20,000 worth of jewelry and other items he had allegedly bought with stolen credit cards in Maryland and Virginia, authorities said. He was wanted in Prince George’s for theft and other charges.

Matos said police have charged Danzo with credit card fraud and are investigating whether he was working alone.

Retail crime increases about 30 percent this time of year as people crowd malls and stores for holiday shopping, according to police departments across the region.

D.C. area police are deploying extra patrols and specialized units, uniformed and undercover, to protect shoppers, employees and businesses.

Hot items this year include iPads and other tablet computers, smartphones, MP3 players and clothing such as skinny jeans, police said.

Many criminals work as part of organized fencing groups, so the person who steals merchandise might not be the person selling it.

“When they’re selling, they just might be selling to one of my officers,” said Prince George’s police Lt. Brad Pyle, commander of that county’s special investigations section, which includes the retail crime unit.

Crimes range from hiding digital cameras in a set of Tupperware while checking out at a store, to skimming a victim’s credit card information and transferring it to a thief’s own card.

Police departments are dedicating more resources to retail crime because it is on the rise, authorities say.

Last holiday season, Fairfax police recovered $200,000 worth of stolen merchandise, an increase from $45,000 the previous year.

The holidays are ripe for retail crime because stores are packed with people and merchandise. Also, police say, it’s a time when people covet things.

“Professionals prefer that time of year because the stores are crowded,” said Montgomery County police Detective David Hill, who investigates retail crime. “It’s easier to go undetected.”