Five teenage boys were arrested last night after a woman was robbed of her purse at a Waikiki beach.

Police said the woman, 20, and her boyfriend were confronted by the boys shortly before 8 p.m. One boy grabbed the woman’s purse and fled on foot. When the victim’s boyfriend tried to intervene, the other boys blocked his way and made implied threats, police said.

A bystander, however, chased down and caught the first boy and retrieved the victim’s purse.

No one was injured.

Of the five boys arrested, three are 17, one is 16 and one is 15. Besides second-degree robbery, one of the boys possessed marijuana and was arrested for promotion of a detrimental drug.

All were released pending investigation.