Professor Albert "Buzz" Scherr, Pierce Law's criminal law expert, tells the Associated Press that New Hampshire has a two pronged test to determine whether a defendant is not guilty by reason of insanity. Read the full story: 

Insanity pleas rare, usually unsuccessful in NH murder cases
Associated Press 

Albert Scherr, a professor at Franklin Pierce Law Center... said New Hampshire law uses a two-pronged test to determine whether a defendant is not guilty by reason of insanity.

First, the defense must show that the defendant suffered from a mental disease or defect. Then, it must show that the murder was a product of that disease or defect.

Neither "mental disease" nor "defect" has been defined by the New Hampshire Legislature or the courts, Scherr said, which empowers juries more than in other states where there are elaborate definitions.