ZDC Controller described a TCAS RA event involving an Air Carrier cleared through a Military Restricted Area; apparently from an unreported/unknown airspace user.

Narrative

I was training on the R-Side at Sector 11. A B737; a departure from BWI; was at 14;000. Aircraft was minimum fuel. We coordinated direct STEIN Intersection. We made a RADAR point to the Patuxent Restricted Area Complex 'Baywatch'. The complex was active up to FL470. They approved the flight through the active military airspace. We noticed a Mode C intruder about 10 miles southwest of the B737; the aircraft was turning and climbing towards the B737. We called Baywatch to verify that they knew; they took a point out on our aircraft coming through their airspace. The Controller's response was 'roger; we're trying to contact the aircraft'. We twice called the traffic; which was an E2; to the B737. We also stated we didn't know what the aircraft was doing; or whether Baywatch had gotten in contact with the aircraft and/or what they were doing if they had. A few seconds later the B737called saying they were responding to a TCAS RA. The Mode C readout jumped from level at 14;000 to 14;900 in one hit. I could not bring up that Mode C intruder on the Falcon replay. So I do not know how close the two aircraft were. Even if aircraft are 'playing' in an active military airspace; having communications with the aircraft inside the restricted area would be advantageous.