A very interesting point to debate, Rachel!
According to the basic tenets of Christianity, David Berkowitz - the serial killer better known as "Son of Sam" - will find a place in Heaven while Mahatma Gandhi burns in Hell...
Berkowitz murdered six people and wounded several others in the course of eight shootings in New York between 1976 and 1977. He has been imprisoned for these crimes since 1977. Berkowitz subsequently claimed that he was commanded to kill by a demon who possessed his neighbor's dog. Although he was raised in a Jewish family he became a "born-again Christian" after his conviction, and, now "saved", will go to Heaven (if it exists.)
Mohandas Karamchand Gandhi employed non-violent civil disobedience to lead India to independence, and inspired movements for civil rights and freedom across the world. But he was a Hindu, and so was not "saved." He desperately struggled to bring a halt to the carnage of sectarian violence that broke out between Hindus and Muslims and for his troubles was assassinated on 30 January 1948 by Nathuram Godse. He was then - according to Christianity - cast into the fires of Hell.
I note that you have asked this question on a few other forums. I didn't bother to read the answers that others provided, instead I shall just offer my opinion: if the person was otherwise a "saved" Christian, then acts committed by them against their conscious, sane will should not stand as a barrier between them and Heaven. Jesus said, "Father forgive them, for they know not what they do" (Luke 23:34) and also said to the repentant criminal "Truly, I say to you, today you will be with me in paradise" (Luke 23:43) - proof, surely, that the criminally insane need not fear the fires of Hell.
I don't believe in Heaven or Christianity, by the way. And the thought of sharing Heaven with Jeffrey Dahmer (serial killer, sex offender, rapist, necrophile and cannibal - and born again Christian) is enough to put me off applying for membership, anyway...