IDAHO FALLS, Idaho -

The United States Supreme Court has refused to accept a case which challenges long-standing and controversial Idaho legislation.

Since the 1980's, defendants in criminal court have not been able to plead insanity.

The case of Delling v. Idaho challenges the constitutionality of this law.

It's a rarely used plea that became infamous during the Ronald Reagan assassination attempt by John Hinckley, Jr.

Hinckley later pleaded insanity in the courtroom.

The case sparked controversy around the nation and led to five states, including Idaho, removing the plea of insanity all together.
 
The term can only be used if the victim knew what they were doing, but could not separate right from wrong.
 
Bonneville County Prosecutor Bruce Pickett explained how Idaho law works without this option.

"Here in Idaho, in order to prove someone is guilty, you have to prove that they knew what they were doing. But you do not have to prove that they knew what they were doing is wrong," said Pickett.

The man at the center of this newest case, John Delling, is a paranoid schizophrenic found guilty of murdering two men he believed were stealing "his energy".

Delling was sentenced to life in prison with no parole, while his lawyers argue it's an excessive sentence for a mentally ill man.
 
The supreme court's decision to throw out Delling v. Idaho is making national headlines.
 
In an op-ed by The New York Times, Lincoln Caplan wrote, "they should have ruled that Idaho violated the constitution by depriving a psychotic individual the right to raise an insanity defense, when that person had no capacity to appreciate that his conduct was wrong."

Fremont County Sheriff Len Humphries weighed in on the issue as well.

He said the insanity plea can have it's place in the criminal justice system, but it's all too often misused by people who are mentally stable.