Someone noticed the guy was mentioned a few times in the reports, and that his mother, with whom he lives, near the Celis family, stated she had not seen her son in 3 days, when interviewed on the 23rd. I am sure she knew whether he had a criminal history, but it almost sounds like she was throwing him under the bus, as one of the "typical" LE questions asked in a neighborhood canvas is "Has anyone you know changed their routine, arrived late for work, had unexplained cuts, bruises or scratches, or disappeared in the days since the abduction?"
Boy, this sure did make the guy sound hinky, and it was compounded by another member discovering his "checkered past." I have to admit that it was looking interesting to me too, and I eagerly awaited more information. Then someone found an arrest record for him for the 20th. While Isabel was reported missing on the morning of the 21st, and was likely not abducted before midnight (i.e. on the 20th), it is quite probable that someone arrested on the 20th would sit in a cell over the weekend awaiting a bail hearing. This not only alibis him for the time during which Isabel vanished, but ALSO explains why he was not seen for several days (per his mom).
A lot of the theories here evolve rather quickly, and it was a matter of a page or so after the first mention of this possible POI that I (and apparently others) had pretty much dismissed him. While there is a slight chance he was arrested in the wee hours of the 20th, and had a full business day before Isabel's disappearance during which he could be arraigned, I believe a closer look at the available information concerning his arrest should resolve this issue.
Now, N.McD still has some 'splainin' to do, IMO. That guy gets around.