IMO, LE has been onto this guy from the time they processed AB's car. Soon after they found her car, they announced that multiple agencies were involved in her case, including US Marshalls, which would suggest that a former convict is involved. Sure enough, it's the US Marshalls Fugitive Task Force that is looking for him (along with other agencies). It would make sense that his DNA is in her car, and they knew his identity then, and have likely been searching for him. Perhaps LE knows far, far more about him and his criminal activity than we do and felt that looking for him quietly could help to keep AB safe. Or. could help to keep him from running.
Of course, the big question is, WHY was he ever allowed to bond out of attempted murder & kidnapping, especially given his long, violent criminal history??????????????