You're right, the other attacks that they know about were close to his home. I'm sure he'll be given a polygraph very soon and either be cleared or not. He's a sexual predator and if he did attack and kill Chandra, you can bet that they'll find DNA evidence on her clothing.
I checked on Mapquest and it indicates 13.7 miles from DC to Aspen Hill and a 44 minute drive. Sounds like a long time for that short a distance, but that's what it says.
I think he was also ruled out because he was seen by numerous people in his own neighborhood on that day. Of course, I;m still wondering if we have the correct date of death, No one seems to want to consider that she was murdered the night before. Someone else in her apartment to throw things off and create an alibi.