Should the mentally ill be treated the same as any other criminal?

Lennie is mentally challenged. He is a child in a man's body. He loves soft, cuddly things but with his brute strength, he tends to accidentally injure or crush things. He kills mice, puppies, and in the end, a human being. But in each instance, these tragedies are a result of his childish mentality and the fact that he truly doesn't know his own strength. 

Lennie never has the intent to harm anything or anyone....

Lennie is mentally challenged. He is a child in a man's body. He loves soft, cuddly things but with his brute strength, he tends to accidentally injure or crush things. He kills mice, puppies, and in the end, a human being. But in each instance, these tragedies are a result of his childish mentality and the fact that he truly doesn't know his own strength. 

Lennie never has the intent to harm anything or anyone. This is a key difference between he and someone who would intentionally hurt or kill. Given this difference (intent), it stands to reason that certain considerations should be made for a mentally ill person who commits a crime and that such considerations should not be given to someone who has no mental handicaps. 

Lennie's mental instability is fully realized when he panics. This occurs when he inadvertently kills Curley's wife. At such a point, he loses control of himself. He doesn't realize how much he can hurt someone. George has done what he can to monitor Lennie and keep him out of trouble. But George can not be there at every moment of every day. George is Lennie's only friend/family. Lennie has no other place to go. So, one could argue that it is society's fault for not helping Lennie and not providing a place for him (to live and work) which addresses his mental handicap and provides a safe way of life for him and those around him.

That being said, if and when someone like Lennie commits a crime, there must be consequences. But a jury and/or judge should take into consideration his mental problems and whether or not the crime was committed with intent, malice, and forethought, or if it was an accident. Such considerations are made regardless of mental ability. A crime which was premeditated is judged more harshly than one committed in the spontaneous heat of the moment. Lennie's mental problems and his panic attacks should also be taken into consideration.