It's improbable and it does complicate things (having multiple people involved in the killings). ALL MOO.
However, this is a highly unusual crime. Since most of this thread has been speculation about various combinations of motive and opportunity, I thought I'd SPECULATE and chime in about scenarios I haven't seen discussed much.
What it someone had a secret? Let's say the secret involved something illegal or highly disreputable or simply very private? What if one of the four victims learned this secret and the secret-keeper believes they told their friend group and that they're being gossiped about? What if they
are being gossiped about? This person could be a frat boy (more on that below) or a sorority sister. This person could have a loyal defender (who is also, for lack of a better word, crazy aggressive and aggro). We have spoken of Neighbor Wars, because we all know that occasionally neighbors kill each other (or even more than one person) over petty things (petty to us). But there can be other kinds of social networks that result in violence - rare, of course, but I believe we'll eventually learn that this rare crime does have reasons behind it (from the killer or killers' points of view).
What if someone had a longterm drug problem? (NOT the victims - the perpetrator). What if the drugs included various combinations of meth (common enough in a college community) and some of the hallucinogens that college students are so into these days? What if a person spent a lot of their waking time fantasizing about violence and killing? They go on the internet and learn about weaponry, how to kill. The meth makes them feel invincible and indeed, meth can temporarily improve certain aspects of performance (like speed), but its ability to give artificial grandiosity and purpose to a user is well known. In the ER, when a person comes in under the influence of meth, almost no one can immediately tell the difference between their mental states, and a manic person - or a schizophrenic person. Psychoses can look very much alike. I haven't done research in an ER in over a decade, but when I did, of the possibilities here in the Los Angeles area, it was almost always meth causing the psychosis (not mental illness - but that did occur as well). And it was common. I was also working in jails at the same time, and we saw a lot of people go straight from a violent situation in their neighborhoods to jail - under the influence of meth. Knife waving, cutting self and others, stabbings (including of police officers), attempted stabbings (often aimed at police), etc. Most were on meth. Some were just mentally ill or drunk. Drunk + meth is a terrible combo.
Third scenario: Frat Boys. Sorry to say, but frat boys do occasionally commit crimes (often under the influence of alcohol or drugs). Some of the crimes are minor (hazing) and some are major (hazing again - because surely even frat boys know that they can kill someone with alcohol, asphyxiation (sitting on chests), or...soy sauce.
Okay, so the soy sauce didn't actually end in a death, but it came close:
A young man at a frat party ingested a quart of soy sauce on a dare and began having seizures when his friends rushed him to the ER.
www.universityherald.com
Here's a link to one of the worst fraternity based crime stories:
Five men will face murder charges over a 2013 incident where a college freshman was beaten up while walking blindfolded across a frozen yard in the Pennsylvania mountains.
www.vice.com
And another:
en.wikipedia.org
The degree of cover-up that can happen in a frat is actually mind-boggling.
(There are way more examples over the past century - but the past decade is enough to peruse if you get interested in frat crime - there's always the Cannibal Face Eating Frat Boy who, of course, was on drugs).
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Having written all that, I am not any closer to a real scenario, except that I do believe this could be either an individual or more than one individual. If more than one individual, my money is on it being related to Greek life/frats/sororities. Both sororities involved in this story were on probation for hazing. Sigma Chi was in good standing, but there had been general hazing issues on campus over the past 7-8 years.
I believe that everything from crazed psycho killer to "personal reasons" killer should still be on the table. And while it seems very odd to me that there would be more than one killer or that the killer had some kind of car or back-up at the scene, I can't discount that either.
My hope is that the killer is not a loner, as they will be very hard to find. If no one knows them well, no one knows they had a certain type knife, no one ever knows that person's whereabouts and they don't always carry a cell phone, it's very depressing. But LE seems optimistic and I still believe they've had a short list of possibilities since Day 1 and that they're still working those leads. I'm guessing the siblings of EC would know quite a bit about EC's situation. If K was the actual target, unfortunately her BFF died with her. A rando who had studied the neighborhood and zeroed in on this house, on that night, is going to be very hard to find.
MOO