If he got to the Beltway insidof ten minutes, at that time of the morning, heading westward, he couldn't have left Montgomery County. But heading eastward, he could have been well into PG County, out US 50, or even up I-95 toward Baltimore. In addition, Georgia Ave. and Connecticut Ave. southbound would have taken him into the District very quickly. The distance to the DC line from the Beltway at Georgia Avenue is not far at all. It would be an easy matter to go down Georgia or even cut over to 16th St., both of which are main north-south drags into DC.
Connecticut Ave. is also a main drag headed into town, but because it swings west of Rock Creek, the drive to I-495 and the DC line is longer than on Georgia Ave. My money is on Georgia Avenue.