Police say a second suspect has been taken into custody.
Montgomery County Police Department reported the development via Twitter. They are assisting the Rockville City Police Department with the investigation.
Mary Jackman was heading down the escalator in the Metro station when she heard the shots. She saw one of the victims, a teenage boy who was shot in the stomach.
"The boy was just covered in blood," she told ABC7 News. "He was hurt really bad...I've never seen so much blood."
Friday - 5/18/2012, 5:41 p.m. ET
ROCKVILLE, Md. - Two young adults were shot and wounded outside the Rockville Metro station, and a suspect was taken into custody.
Metro spokesman Dan Stessel says the shooting was reported just after 2:30 p.m. Friday outside the station but on Metro property.
Police say the shooter was arrested less than 10 minutes after the call came in. The shooter was taken into custody at a nearby Shell gas station.
A weapon was recovered. Police believe the suspect and victims may have known each other.
The first victim was shot in the tunnel exit of the Metro. A second person was grazed by one of the bullets.
Police say injuries to both victims are non-life-threatening.
A second person who was with the suspected shooter at the time is being called a person of interest.
The victims' names were not immediately released.
The shooting did not affect service on the Red Line, where the Rockville station is located.
The east side of the station was cordoned off temporarily with police tape. WTOP reporter Adam Tuss saw up to 9 flags indicating multiple shots were fired in the incident.
Witnesses at the station say they heard loud cracks and pops.
WTOP's Adum Tuss and Max Smith contributed to this report. Follow Max, Adam and WTOP on Twitter.
(Copyright 2012 WTOP & The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)