IF more disturbing elements of this crime prove to have taken place...
I believe control is the central issue at play here.
To consume or engage sexually with the remains of your victim demonstrates an urge to fully control that person, likely resulting from a feeling of personal powerlessness. Let's imagine for a moment that Stephen was fixated on Lauren for a long time, living next to her, working along side her in the FedSoc at Mercer, but never truly able to engage with her on a personal or romantic level. Most likely he never voiced his feelings for her to her directly, but perhaps spoke frequently about her to his mother. He felt she was unattainable, she'd never return his feelings, he'd never HAVE her in life. Perhaps her life force itself was overwhelming to him, because deep down in his psyche, Stephen could be extremely controlling. No consenting partner, especially not an independent and driven young woman such as Lauren, would be suitable for him as he would require the utmost submission and autonomous control over another individual. This is often the case with killers who engage in these post-mortem acts of cannibalism and necrophilia. Only once their victim is dead can they truly actualize their fantasy.
For some killers, the act of defiling their victim's body is an extension of the sadistic acts and degradation they inflicted on their victims pre and peri-mortem, as in the case of Ted Bundy. For others, such as Jeffrey Dahmer, it is the main event. I imagine McDaniel falls into the latter category. He "attained" Lauren in killing her, and cemented his sense of ownership over her entire being [in his mind] by deconstructing her person-hood, literally and figuratively, after death. This is typical of lust murder, as the killer seeks to remove the humanity of his victim through mutilation and disfigurement. The dismemberment itself indicates rage, resentment, but more interestingly it indicates that the killer was threatened, intimidated by the victim. To strip the victim of her identity is to neutralize the threat and exercise ultimate control. It's very personal. When such acts are committed in stranger homicides, such as in the case of Jack The Ripper for instance, the victim is representative of something personally threatening to the killer. In this case, Lauren herself was somehow a threat to Stephen's psyche. IMO, the threat stemmed from the power he perceived her to have in life. If he was obsessed with her, in his mind she held an unacceptable amount of power over him, and in killing her and then destroying her body, he re-asserts his own control. He is aroused by that satisfaction derived from absolute control over someone formerly so out of reach, he can now do as he pleases.
Finally, if cannibalism indeed took place, it would be the penultimate act of control and possession of his victim.
IF it went down like that, I imagine he was high off his actions for several days. The extensive cleaning and obstruction was another way for him to get off on the control he continued to exert over his victim's fate. His downfall was ultimately that he was too greedy with her remains, too indulgent of his urges, to do what needed to be done. He literally waited until the last possible moment to discard the last bit, despite the overwhelming risk involved. Hopefully that means he did a poor job of cleaning up the evidence he left on her body, especially if he originally planned to dispose of them in such a way that they would never, ever be recovered prior to decomposition. If the bleach rumor turns out to be true, that was probably his hurried attempt at making sure he rid the body of evidence, and it probably wasn't as thorough a job as he would have liked. His nerves went into overdrive when he saw cops looking for her Wednesday, so he inserted himself into the search and investigation promptly to control, to whatever extent he could, the flow of information and get access to the facts on the ground. I wouldn't be surprised if those involved in the search, cops and civilians, could tell us in retrospect little things he tried to do to direct the search effort away from key areas.
Getting on camera to discuss Lauren's whereabouts was terribly revealing, and terribly bold. I'm sure he derived some satisfaction from that as well, still holding out the belief that he'd never be found out, linked forever to her memory however due to that interview. Imagine how satisfied he'd have been if he'd never been a POI and his face in that interview would come to represent that fateful day in Lauren's legacy...what a fast one he'd have pulled.
JMO
