With regard to lying to get a lesser punishment, I was reading this old article on Slate (At last we know why the Columbine killers did it. - Slate Magazine) regarding Eric's lying and apology about the van, and psychologists Dwayne Fusilier and Paul Eckman's interpretation of it:
Harris claimed to lie to protect himself, but that appears to be something of a lie as well. He lied for pleasure, Fuselier says. "Duping delight"—psychologist Paul Ekman's term—represents a key characteristic of the psychopathic profile.
Harris married his deceitfulness with a total lack of remorse or empathy—another distinctive quality of the psychopath. Fuselier was finally convinced of his diagnosis when he read Harris' response to being punished after being caught breaking into a van. Klebold and Harris had avoided prosecution for the robbery by participating in a "diversion program" that involved counseling and community service. Both killers feigned regret to obtain an early release, but Harris had relished the opportunity to perform. He wrote an ingratiating letter to his victim offering empathy, rather than just apologies. Fuselier remembers that it was packed with statements like Jeez, I understand now how you feel and I understand what this did to you.
"But he wrote that strictly for effect," Fuselier said. "That was complete manipulation. At almost the exact same time, he wrote down his real feelings in his journal: 'Isn't America supposed to be the land of the free? How come, if I'm free, I can't deprive a stupid f---ing dumbshit from his possessions if he leaves them sitting in the front seat of his f---ing van out in plain sight and in the middle of f---ing nowhere on a Frif---ingday night. NATURAL SELECTION. F---er should be shot.' "
The article concludes with this paragraph:
Their (psychologists and psychiatrists cited in the article) view of Harris is more reassuring, in a certain way. Harris was not a wayward boy who could have been rescued. Harris, they believe, was irretrievable. He was a brilliant killer without a conscience, searching for the most diabolical scheme imaginable. If he had lived to adulthood and developed his murderous skills for many more years, there is no telling what he could have done. His death at Columbine may have stopped him from doing something even worse.