Yes, he "had" one in the same sense that he probably had a stuffed toy at home, it wasn't used in the crime, so it is irrelevant and demonizing said possession is clearly more about seeking to control that item than anything justified by the crime. . . which did not involve the AR15.
But to answer your question, the AR is a handy little rifle with good ergonomics which is easy for beginners and women to shoot well, excellent in home defense when equipped with a white light and red dot of some variety, the fragmenting nature of the rounds means they will likely go through one side of a wall and frag before meaningfully penetrating the second as most walls in homes have two sides AR15's can be fired with lower risk than weapons such as a shotgun where the weight of buckshot can carry through with enough velocity to seriously injure people on the other side of walls. They are used extensively in shooting sports. They have become increasingly popular among hunters who enjoy the modularity of the AR, allowing them to switch from a long barrelled .223 for prairie dog to an acceptable deer caliber carbine like 6.8SPC. There really isn't any gun on the market that has the ability to as easily switch between various calibers and usage (upper) while retaining the same gun (lower) almost like a golfer's bag of clubs. They even have blank firing attachments for launching golf balls for that matter! Since pretty much nothing on the market matches its versatility the short answer would be a responsible gun owner could fill any lawful use need with an AR.