Still making my way through The Storm of War, but I've also started on Maury Terry's The Ultimate Evil.
Terry's thesis is that David Berkowitz alone was not responsible for the "Son of Sam" killings, as is popularly believed. Instead, there was at least three killers involved in the crimes, and while Berkowitz is certainly guilty of some of the killings, he was performing them under coercion (Berkowitz's bizarre behaviour during the killings, including numerous arson attacks designed to draw attention to himself and land him in prison on a lesser charge, are indicative of this). Furthermore, the group killings have a cult undertone to them, and are related to the Process Church of the Final Judgement (or their Four P splinter group...or both) and a number of murders on the West Coast, including possibly those of the Zodiac Killer.
I have it on good authority from someone who has read the book, and is well connected in the New York occult scene (indeed, he was in New York during the murders and went to the same school as Berkowitz, albeit at a different time) that while Terry's analysis is poor, due to his lack of knowledge of the occult and the complications that arise from Berkowitz's testimony, Berkowitz having converted to a fundamentalist form of Christianity while in prison, his raw data is unassailable and, if taken on that evidence alone, makes for compelling reading.
I'm also inclined to believe some elements of this, if only for the reason that, as serial killing, the Son of Sam murders are so damn odd. Serial killers almost never use guns, especially not in their more mature "cycling" phases of violence. The literature on this is quite clear...speaking of which, Berkowitz was remarkably well read on the psychology of serial killers, including a book written by the psychologist who examined him after his arrest. And the murder of several people involved in the case after Berkowitz was already in prison is pretty much concrete proof that, if nothing else, he had accomplices.