office creeper
n. A person who sneaks into an office building during business hours to steal personal items and equipment.
Other Forms
Office creepers — thieves who walk into the workplace looking for pricey laptops or purses — are increasingly becoming a problem in the business world. Since laptops became commonplace in the mid-1990s, neatly dressed criminals have found a new crime where they can turn a quick profit.
—Mark Niesse, “Upscale thieves take advantage of witless cubicle-dwellers,” The Associated Press, October 15, 2003
In Stamford, Conn., and nearby suburbs, police are searching for a team of well-dressed men suspected of stealing as much as $100,000 in laptops and other office equipment last spring. The thieves apparently entered offices at the end of the day, just as employees were leaving and cleaning crews were arriving.

This summer, a Boca Raton, Fla., police spokesman says, a well-dressed burglar chatted with office workers at an elevator, bidding them "a nice day" while walking off with three laptops.

In the past 18 months, an Atlanta task force of police officers and property owners set up to combat "office creeping" … has cracked 11 cases but is still looking for seven other suspects, including one believed to be a cross-dressing man. "About every property around metro Atlanta has been hit by an office creeper," says Jim Carsten, director of security for an Atlanta-based landlord, Cousins Properties Inc., and a member of the task force, known as Metro Tech.
—Dean Starkman, “To Stop That Laptop Thief, Hold the Smile, Not the Door,” The Wall Street Journal, September 24, 2003
1990 (earliest)
"Anybody can gain access to the building with a business suit and create mischief," warned Aydin (Turk) Bircan, president and chief executive officer of ISS Security Services Inc. in downtown Los Angeles. "In the daytime, the office buildings are quite vulnerable." …

Tenants seek protection from a wide range of undesirables such as disgruntled ex-employees, crazed clients, dishonest office workers and organized groups of thieves, known as "office creepers," who make their way through whole neighborhoods.
—Ron Galperin, “Office buildings stepping up security services,” Los Angeles Times, June 24, 1990