As I have pointed out in previous postings, it appears that Murray was evincing symptoms of psychosis (hearing voices, for example). Was he not receiving treatment?
It is very, very easy to second guess what went wrong. Murray's father is a respected research neurologist--how could have missed Murray's symptoms? I can see several possible explanations.
1. Maybe his father saw the symptoms, and tried to get him help. But thanks to the ACLU, you can't force an adult into treatment except under rather extraordinary circumstances, and even the threat, "You need to get help or move out" is a hopelessly painful step. I've seen this situation close up, and no parent wants to make a agonizing demand like that--for fear that the mentally ill child will move out--and get even worse.
2. Schizophrenia isn't a binary situation. Some people are obviously psychotic; others have good days and bad days, and it is very easy to mistake the bad days for laziness, or a lack of ambition. Simple schizophrenia, for example, has a symptom list that seems to fit published accounts of Murray's behavior, and might explain why his parents could have failed to see mental illness (which is always painful to face):
An uncommon disorder in which there is an insidious but progressive development of oddities of conduct, inability to meet the demands of society, and decline in total performance. Delusions and hallucinations are not evident, and the disorder is less obviously psychotic than the hebephrenic, paranoid, and catatonic subtypes of schizophrenia. The characteristic "negative" features of residual schizophrenia (e.g. blunting of affect, loss of volition) develop without being preceded by any overt psychotic symptoms. With increasing social impoverishment, vagrancy may ensue and the individual may then become self-absorbed, idle, and aimless.
3. There is a tendency in fundamentalist Christian circles to refuse to acknowledge that mental illness can afflict Christians. Obviously, this isn't the norm; most fundamentalist Christians do know better. But over the years, my wife and I have met more than a couple of fundamentalist Christians who simply refuse to admit that mental illness is something that requires more than prayer. It may require medication, since many of the more severe mental disorders are biochemical in nature--no different from diabetes in that respect.
UPDATE: A reader tells me that a caller to the Dennis Praeger show this morning claimed to know the family, and that Murray was being medically treated--but without success.