Texas Executes Cop Killer:  61-year-old Robert Jennings was put to death Wednesday for the 1988 murder of a 24-year-old Houston police officer during a robbery.  The Associated Press reports that Jennings won a stay in 2016 to review claims that he suffered brain damage, had a troubled childhood and that he was remorseful for the killing, but his request for additional delay this year was turned down.  Jennings, a twice convicted robber, began a crime spree shortly after his parole in May 1988 which included 10 robberies.  In July of that year he entered an adult bookstore to rob it when he confronted Officer Elston Howard, who was in the process off arresting the owner on a pornography charge.  Jennings shot the young officer twice in the head, then shot him two more times after he lay bleeding on the floor.  Jolie McCullough of the Texas Tribune reports that Jennings expressed remorse for the murder to the officer's family prior to his execution.  The appellate review of his conviction and sentence, where his guilt was never at issue, took longer than Officer Howard had lived.