I do think that McD targeted Lauren because she was significant to him, and that this was not a random, chance event. But many of the aspects of the murder make me wonder if perhaps McD was a serial killer in the making; if whether the only reason there are not more victims is because he got caught the first time he tried.
This article summarizes the progression of serial killers, and a lot of it is eerily reminiscent to McD. Except that McD is something of a weird amalgamation of the "organized" and "disorganized" offender types, showing traits of both. The profile of the type of serial killer McD seems to fit, from the article, also hits close to home:
In summarizing both developmental theories and individual case studies of serial murderers ... the following picture emerges: an individual who spends excessive time in a reverie of deviant fantasy and has a tendency toward isolation, a need for totally submissive partners and a preference for autoerotic pleasure. (S)uch an individual will have a lack of healthy relationships and subsequently must depend on fantasy for gratification. At some point, mere fantasy becomes an insufficient source of pleasure for the potential offender. ... During a burglary, the offender may steal fetishistic items for sexual pleasure, such as undergarments. When this fails to provide sufficient satisfaction, the offender may progress to rape and ultimately murder.
McD's theft of the condoms seems like a significant clue in figuring out what was going on with him. A lot of people, here and elsewhere, have commented that Lauren's murder is not the kind of offense that someone just starts out with. But the murder was not necessarily the start -- it could have been the result of a very quick progression. Sexually motivated burglary is often a precursor crime, and it very much seems like, to McD, the single condom he stole from each apartment was both a voyeuristic and a fetishistic act -- knowing exactly where and how his neighbors kept an item they used for sex, and taking the item for himself, gave him a thrill.
The excerpt from
this book has some more specific examples, showing a fairly strong link between serial killing and cat burglaries.
Lauren's murder has gotten so much attention, in part, because it is very much not a normal crime, and doesn't fit with any usual pattern. But I think maybe the reason it doesn't seem like the usual acquaintance murder is because it wasn't one at all -- it was a serial killer's first hit.