"What was the LEO thinking....nothing I guess."
He appears to have been thinking that he had the best part of a week before anything might happen. The little CYA article that the Norman PD put out actually dug a deeper hole. When this off-duty police officer overheard the odd and disturbing conversation between Hinrichs and Ellison, the store owner's son, he only called in to run the tags, and didn't react because the tags came up clean. Also, from this article that was intended to absolve the officer, he has yet to file a written statement, which, according to police chief Younger, would have "eventually been forwarded" to federal authorities.
The unintended upshot of this article: no sense of urgency whatsoever. In light of the reportedly substantial amount of ammonium nitrate found in Hinrichs and Cheeba's apartment, they are very, very lucky that they don't have a repeat of the Murrah Building, but with far more people, hanging over their heads.
Let's just hope and pray that this woke them from their slumber.