Witnesses describe him as a thick black man, maybe 200 pounds, who wears dark clothes, a mask and gloves. He mostly targets teenage girls in the early morning hours and carries a handgun.

''We're trying to express how important it is to keep your home secure,'' said Miami-Dade Police Major Elizabeth Buchholz, head of the department's sexual battery unit.

Investigators believe this one man may be behind at least 13 cases of intruder sexual assaults or break-ins in North Miami-Dade and South Broward since January.

His apparent target was 14 years old. He climbed on top of her, but when she screamed, family members came running, the Broward Sheriff's Office said.

Miami-Dade police have been issuing news releases about a repeat intruder in Miami Gardens since at least May. In the sensitive world of investigations, detectives say they've tried to walk delicately between causing panic and feeding the stalker's ego.

Uniformed patrolmen have been alerted. Fliers have been distributed. Miami-Dade police say they're investing ''a great deal of resources'' to catch the stalker.

Last week, detectives believe, he was the intruder who used lawn furniture to climb through a window of a North Miami home and sexually assault a 14-year-old girl.

In Miami-Dade, sexual battery detectives have identified seven cases in Miami Gardens and three others elsewhere in the north end of the county. They also are examining two other cases that may be related.

On Friday, officials again stressed safety measures: Keep doors and windows locked, know your surroundings and, if possible, check the Internet for a list of sexual predators in the neighborhood.

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