I'm no longer a DC local, but I was as recently as a few months ago.
Lyft, Uber, cab, etc. are all options. There is a red line WMATA train stop (Woodley Park) about 3/4 of a mile from where they lived. There are other bus routes within a few blocks, although it's very unlikely he could easily get there via bus from where he lived. If he took public transportation, the train is much more likely IMO.
I've always speculated that he got a ride from someone, partially because I still think there were others involved.
I'm honestly shocked we still don't know these kinds of details about this crime. That area of DC houses the VP, ambassadors, and many wealthy families. The fact that they lived across the street from the Ambassador of Australia and within a few blocks of the VP's residence, and there's still seemingly no video evidence of him arriving or leaving (that we know of, at least) is honestly shocking to me.
Additionally, if they suspected he took the train, they should have been able to get security videos from the likely stations he used.