U.S. Capitol Police arrested a man at a checkpoint at the Capitol Tuesday afternoon allegedly in possession of a large quantity of Ecstasy pills, prompting a joint investigation with the Drug Enforcement Administration, ABC News has learned exclusively.

The man, identified by USCP as Dennis A. Silva, 25, has been charged with possession with intent to distribute a controlled substance after he alarmed officers when he parked his Honda Civic at a barricade to the East Plaza of the Capitol and began photographing them.

Silva produced an expired New York driver's license, police said, initiating his arrest.

"Officers approached the vehicle and conducted a name check on the driver which revealed no valid permit in any state," Lt. Kimberly Schneider tells ABC. "The defendant was placed under arrest."

A USCP report states that when Silva was searched the officer "discovered a clear plastic bag with multiple colored pills on the Suspect's person." According to the report, a field test conducted on one of the pills tested positive for MDMA, also known as Ecstasy or Molly.

A source close to the investigation says that officers continued searching Silva's front seat as legally permissible, but it became apparent that a search warrant was needed to fully search the vehicle so the search was stopped. It's unclear whether all of the pills were MDMA.

The vehicle was then secured off-site by the USCP for further processing after it was swept for explosives and pathogens by K-9 and nothing hazardous was discovered.

Almost 24 hours after the incident, USCP was still seeking a search warrant from a judge at DC Superior Court to fully search the vehicle, which officers observed was overloaded and weighed down. DC Superior Court refused to comment on a pending warrant, but confirmed that Silva was on a lockup list and expected to be presented in court later today.

Sources indicated more charges are likely once authorities determine exactly what Silva possessed.

DEA's role in the investigation is unclear but a source said the agency became interested in the case because of the alleged large number of pills Silva allegedly possessed. DEA did not respond to repeated requests for comment.

A source at Capitol Police did not know whether Silva had any notable connections or affiliations to gangs or organized crime.

*This story has been updated to reflect a field test revealed a pill to be MDMA, and to specify Silva's vehicle is a Honda Civic.