A suspect has been arrested in connection with the third violent incident this year in the Bethesda tunnel that is part of one of the most popular biking and hiking trails in the Washington area.

Montgomery County police said Friday that a 16-year-old male from Rockville was arrested and charged with attempted robbery and second-degree assault in a Sept. 29 attack in the tunnel under Wisconsin Avenue.

That attack followed two similar incidents that took place in July. In one, the victim was punched in the face after refusing to surrender his belongings. In the other, the victim was robbed and punched, authorities said.

The tunnel is a key segment on the Capital Crescent Trail, which runs between Georgetown and Silver Spring and is heavily used for recreation and for commuting.

On an online discussion forum maintained by a group of trail users and supporters, the incidents in July were described as unusual. “This is the first violent crime that we are aware of to occur in the tunnel since it opened for trail use in 1998,” read a post on the Coalition for the Capital Crescent Trail site.

“We believe that the trail” and a nearby park “continue to be reasonably safe,” the posting continued. However, it advised trail users to be aware of their surroundings, particularly around the tunnel.

In the most recent incident, police said two male 16-year-olds and another juvenile were walking on the trail about 8:50 p.m. when about five or six male teenagers approached. One of them grabbed one of the victims and demanded money. The second victim tried to intervene but was punched in the head and face.

The victim and his attacker were separated by the others, and the attacker and those with him left without getting any money, police said.

The victims went home, and the one who was struck and injured was taken to a hospital for treatment.

Police said they received a tip and on Thursday arrested the Rockville youth in the incident.

The first of the two earlier incidents occurred about 7:45 p.m. July 6. Two people, one wielding a knife and wearing a bandanna over his face, approached the victim in the tunnel and demanded his backpack. The victim refused the demand and was hit, authorities said.

The second incident occurred about 8 p.m. July 20. The victim in that incident was confronted by four teenagers, authorities said, and one punched him in the face. After he fell, his wallet was taken and the teenagers ran from the scene.