O refers to those aspects of an offender's behavior which are necessary to successfully complete the crime, e.g. wearing gloves so as to avoid being identified. Signature refers to those aspects of his behaviour which are only necessary to fulfil his emotional needs, e.g. taking off his gloves just before strangling his victim because he needs to feel her skin.
Stewart Wilken liked to face his victims while sodomizing them so that he could watch their faces as he strangled them. He referred to their last moments as the 'jellybean effect' (Pistorius, 2000, 2002). Their eyes would bulge, their lips swell and their tongues protrude from their mouths. It was at this moment when he would ejaculate.
There are three base motives of the serial killer: domination, manipulation and control (Douglas & Olshaker, 1997). Wilken felt inadequate and inferior, but when he was killing, his victims were completely under his control. Particularly at the moment of the "jellybean effect," he was vividly aware that he had power over their life or death. This sense of power is intoxicating, and he felt omnipotent (Pistorius, 2000). This was the moment he felt alive and divorced of his usual inadequate existence. By being in control of another person, he felt as if he had control over his own life. Wilken often became enraged when his victims demanded their payment or complained that he was hurting them, and he would kill them almost immediately. He felt that they were trying to take his control and would not have it.
Prof. Tuviah Zabow, who evaluated Wilken's ability to stand trial and distinguish between right and wrong, described him as a sadist. Certainly, anal rape is classified as sadistic (Douglas & Olshaker, 1998b). His preference for the "jellybean effect" is even more so. But Wilken again does not fit neatly inside the box. Sexual sadists like to torture their victims in elaborate fashion, usually over protracted periods, and they relish any cries of pain (Michaud & Hazelwood, 2000). Wilken seemed to be motivated to kill as soon as his victims complained of pain. Perhaps because he remembered his own pain?
Be that as it may, his sadistic pleasure in watching his victims, including the boys, die, stands in stark contrast to his contention that he wanted to save them. However, it does not necessarily deny its truth. Serial killers do not think the same way that "normal" people do. While it seems contradictory from a "normal" perspective, it need not be from Wilken's.