A good vacation book to read is Meyer Levin's fictionalized book about that case, Compulsion. It's gripping, and pretty well sticks to the facts of the case -- written as a novel in order to avoid lawsuits IIRC (U.S. libel laws differ from Canadian ones in important ways, and the fact that the story you write is true is not a protection there).
But while Loeb and Leopold thought they were geniuses, they actually were in the near-genius range intellectually, while there's no evidence whatever that DM or MS are anything but average in the IQ department. Both indeed may have learning issues, and the more I think about it, the more convinced I am that DM exhibits signs of fetal alcohol damage (no worries, it does not exculpate a person from criminal responsibility -- it's not a mental illness). It could go together with psychopathy, if he is diagnosed with that, or could be separate. MB would know, of course, and an fMRI could probably show typical areas of damage. DM's verbal prowess, so vastly superior to his completely moronic grip on finances, is a classic sign, as is his compulsive sexual promiscuity, his inability to plan realistically, to take consequences into account, to follow through on things ("executive function" in the jargon of the field), to make and keep friends of his own age, and on and on.
MS does not strike me as either psychopathic or FAS, just a common criminal type. The fact that he had been in trouble with the law from early days, despite a fairly strong family (apparently) and did poorly in school, may indicate learning disabilities or behaviour disorders in his early years, hard to know. It's not unusual for kids with LD to run into trouble with the law as early as elementary school, due to poor impulse control, running with the wrong crowd, feeling like failures due to academic struggles, and so on. Not an excuse, but social problems are very common among youngsters with LD. Programs like those of the Integra Foundation can help prevent them escalating. I don't know if any of this applies to MS, but if some does, he has a better chance of rehabilitation over the long term. For FAS or psychopathy, the prospects of significant change is slim to none.
