Some more detailed reporting today reveals that you're probably right: they first identified the set of people or vehicles in the area/time. Then they collected

Some more detailed reporting today reveals that you're probably right: they first identified the set of people or vehicles in the area/time. Then they collected DNA and cross-checked the DNA with the set of area/time suspects. That led them to the suspect. Everything after that was just waiting to see if he would incriminate himself further? or perhaps just to make the movie plot more interesting?