In Australia, a person may be judged to be 'not guilty due to insanity, rather than the US version of “guilty but insane”" Such pleas are so rarely successful that they are rarely offered.
Our most prolific mass murderer is Martin Bryant. In 1996,at Port Arthur Tasmania he shot dead 35 people and wounded 23. He was given 35 life sentences without possibility of parole.
Bryant is ‘intellectually challenged’ , but it was determined he was fit for trial.
Bryant used an AR-10 semi automatic rifle.
As a direct result of that tragedy,tough new gun laws were introduced federally within a few weeks.Today it is very difficult to own even a hand gun in Australia. In what is surely a coincidence, since those laws were passed, there have been no mass shootings in Australia. 
Below couple of clips with Aussie comic Jim Jeffries, who is very popular in the US. The topic; gun control. Worth watching if you haven’t seen them: (13M views)
