Just going to go out on a limb here and say:
I have a THEORY that JLM Jr has been the prime suspect on a very short list re: Morgan Harrington and possibly others for quite some time now. I suspect that LE has been looking into his background for a few years now yet had no way to legally acquire his DNA to submit it into CODIS. They needed for him to be charged with a felony which would allow LE to obtain a DNA collection, upon arrest.
IMO, they knew he was a cab driver in 2009, they likely knew about the previous dropped sexual assault charges at LU & CNU and they probably were keeping tabs on the vehicles he drove between 2009 and today. I'd be willing to bet that he was pulled over on all those vehicular offenses in the same way that RAT was pulled over so many times. IMO, I believe they were doing what was allowed, within the law, to keep tabs on JLM Jr and hope that he would screw up before another girl got injured.
Honestly, I believe he knew that LE was looking at him. IMO, he parked that junker of his almost practically right in front of the CPD HQTRS, on Sept 12th, 2014 out of shear defiance. If he abducted and murdered HG, he probaby got a big thrill out of doing it right under CPD's nose and parking lot cameras. (ALL IMO, of course)
I don't see a conspiracy or a neat little package to frame the big guy. I see LE stratagizing, developing and cataloging a case investigation on their prime suspect. When HG disappeared and CCV showed her on video at the DTM and then JLM Jr crosses right in front of the camera, LE saw him immediately and CPD went into high gear to track him down, get all the warrants and finally get this guy.
I think some of Longo's outrage was that JLM manged to do this almost right in front of the CPD HDQTRS.