· Professional gang carries out 50 break-ins
· Criminals leave behind no DNA or fingerprints

The rich and famous of Los Angeles protect their mansions with high walls, security cameras and sophisticated alarms. But it has failed to stop a small team of burglars who have hit about 50 homes over the past year and got away with an estimated $7m (£3.4m) in cash, rare books and jewellery.

There is a break-in in Los Angeles every 15 minutes. But most of these are opportunistic, often drug addicts going through open doors or windows.

The ones in Los Angeles' exclusive enclaves are different. Police reluctantly described the burglars as "professionals". A councillor called them a "two-man crime wave". So far they have left no significant clues: no fingerprints, no DNA, no alarms triggered and only fuzzy camera shots. And they appear to have been disciplined enough not to sell any of the jewellery or other traceable items through the usual "fences". Police say that, as far as they know, none of it has yet appeared on the black market.

The police have so far refused to provide details of how the two men - possibly three - manage to gain entry so successfully and so often. The men, wearing ski-masks and black clothing, are quick.

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They have concentrated solely on exclusive districts such as Encino, Beverly Hills and Bel-Air. Victims have included celebrities, sports figures and tycoons. Lieutenant Ray Lombardo, a Los Angeles detective, told the Los Angeles Times: "It is a target-rich environment in the hills, and these guys know it and know the homes and area. I hate to call them it, but they are professionals. They aren't opportunists."

He added: "They take cash and jewellery and leave behind guns and valuable watches. They know what they are seeking."

Jack Weiss, a councillor who represents one of the areas that has been targeted, said: "These guys are a two-man hillside crime wave. They are quick-hit artists. They are clearly knowledgeable and sophisticated."

The police have officially declined to name the victims. But they include: the Duran Duran guitarist John Taylor and his wife, Gela Nash-Taylor, president of Juicy Couture; the basketball player Cuttino Mobley; the country music stars Tim McGraw and Faith Hill; the former head of Paramount Pictures, Sherry Lansing, and her husband, the Oscar-winning director William Friedkin.

While the police have refused to give details, one officer said the burglars had climbed through a second-floor window in one burglary, thereby evading the alarm system, and, in another, had used a brick to smash patio sliding glass doors, even though these are normally among the first areas in which alarms are installed. Many people with alarms either forget or cannot be bothered to arm them when they go out. The burglaries usually take place in the evening, or at weekends, when residents are away.

The police have issued photos from a security camera showing two muscular men without masks. The police put their ages at between 25 and 30.

There was a similar plague of burglaries four years ago but no one was caught. About five people were in that team, police believe.