That is an amazing tale of woe! I'd say that the range was lacking in supervision for sure as far as the culprits go but how embarrassing for the gun owner! I can honestly say that I have never left a firearm unattended anywhere and here is why: The United States Marine Corps! To forget a rifle, or drop it, was tantamount to treason when I was in boot camp. Many, many push-ups and a hellish verbal assault were the rewards for forgetful recruits.
I will likely recall until the day I die an incident that occurred when I was in MCT (Marine Combat Training) just after boot camp. I had been stuck as a squad leader and the Sgt. instructing was having me show him where my guys were digging two-man fighting holes in the soft Carolina sand, stripped down to skivvie shirts in the humid July afternoon. We came to a hole where they were almost down to the required depth and the instructor recalled something he needed to tell someone. He sent one of the Privates digging to run off with the message. We were still pretty wet behind the ears, new to actually being Marines and at the words of the Sgt., he took off running. The guy left his M16A2 on top of his ALICE pack and as I opened my mouth to yell to him, the instructor told me to shut up. He then had me lock the bolt to the rear on this guy's orphan rifle, drop it in the hole and then his partner and I buried it! Buried it and were stomping on it with our own rifles raised over our heads, singing the Marine Hymn, when the rifle leaver returned. The look on his face told us he knew where that oh so previously clean weapon was. I hated that day, man.
Sorry to run off topic, you know how those Gyrenes get. Here's hoping they nai the thieves but what will happen to the owner? Keep us posted!