I have run many CNC machines in production and tooling situations and I realize that one wrong keystroke can cause BIG problems. Machines do not have spell check to check your typing.
I believe the best thing to do in a case like that is ask the operator/machinist. You do not need to check the control, you have an eyewitness.
I would talk to the operator, spell out the consequences of the mistake. If disciplinary action is due, tell the person that you expect him to be honest with you and take the punishment. Explain the situation, let him know that if you can't find out what caused the crash you may have to spend unnecessary money looking for a problem that does not exist. If there is a glitch in the machine and you assume operator error without dealing with real problem, it is a sleeping giant waiting to rear it's ugly head when least expected.
I have found that an environment of trust and honesty are the best way to run an organization. If the machinist is afraid of loosing his job for an honest mistake you have a bad work environment and you will spend too much time fixing things that are not broken. You will also lose the opportunity to explain and teach other machinists about problems and characteristics of equipment that need to be considered to make safe and productive machining.
If you must protect the machines from the machinists try a video camera on the machines 24/7 then you can replay the tape and know what happened. There are keys on the control, I believe that you can lock the control to prevent edits or employ the buddy system so no one can do offsets without a witness.
There is alot of information that can be collected from the smashed tools and machinery that tell stories also.
Good luck.