A robber approached a 70-year-old woman on the street in Prince William County over the weekend and grabbed a necklace from around her neck, county police said. It was the third such incident in the county in a week.

The robberies occurred relatively close to each other in the Manassas area between 4 and 6 p.m. In each case, the description of the robber was similar: An African American male, 15 to 20 years old, 5-foot-10 to 6 feet tall, with a thin build.

In the most recent incident, on Saturday, the woman was walking home in the 10100 block of Portsmouth Road when the robber approached and pulled on her necklace. It broke, and he took it and ran to a waiting car.

Two days earlier, on Thursday, police said, a 44-year-old woman was walking home in the 10900 block of Coverstone Drive when someone approached and grabbed for her necklace, knocking her down. Police said the necklace broke, and the robber fled.

On Wednesday, a 56-year-old man said a robber approached as he was walking near Hiram Court and Notre Dame Street. The robber assaulted him, seized a necklace and fled.