take shape. >> i'm hearing a lot of very negative and at least heavily psychologically abusive things, but it's not answering what's wrong with this kid, cause he's incredibly sweet. how does he walk into a room with a shotgun, this kid? and it doesn't add up. i mean, i'm totally, totally puzzled. and that's when i bring in vicary. >> reporter: dr. william vicary, a forensic psychiatrist and graduate of harvard law school, agreed to meet with the brothers in jail. he knew going in, police believed lyle and erik killed their parents for money. >> but based upon the dozens of parricide cases that i had worked on in the past, that's the exception. that's not the rule. the rule is that something horrible is going on in the family. >> reporter: and something was going on in the menendez family. something very secret. but what was it?