I agree, otherwise he would have killed the children also. This was a track and kill operation in my opinion which may be totally wrong. This was not a sophisticated killer. Covering your plates with tape is just asking to be stopped. Steal plates the night before from long term parking at the airport and use them.
He could have removed the tape after he was some distance from the park. But if he put the tape on before the attack it appears he went there planning to kill someone. They said the family had only recently moved to the area from California (so not a family he had had run-ins with and hated). Hope the daughters got enough of a view of him to help the police.
My guess is the kids didn’t want to move to Arkansas so they paid someone to kill their parents