Police know the exact model and color of the truck the killer was driving. It's an older model, black, four-door Nissan Frontier. Through DMV records they must have identified all owners of every one of these trucks in south Texas. The killer should realize this and contact the District Attorney. He or she should make a deal with the DA now because he or she will eventually be arrested.
It's possible the killer traveled across state lines in that older model, black, four-door, Nissan Frontier. IMO, the family should push the sheriff's office to seek FBI assistance.
Will any Harris County deputies travel to the huge Star Wars cosplay event in Chicago this weekend for surveillance and to question participants? Imo, it would be tragic if deputies missed this opportunity and the killer (if he or she attends) had a magnificent time at this cosplay event.