IMO every killer is an amateur at one time. First time for everything adage.
I disagree that this was a psychotic serial killer. Serial killers have types. If you look at the women victims of a serial killer they all look enough alike to be sisters or brothers. An SK carefully watches for someone who fits his "type". A SK doesn't pick a random house and kill two blonde females, one brunette female and one male. Some of the people who have been mentioned on here are not bona fide serial killers. They are mass murderers, family annihilators or spree killers, not true serial killers like Bundy, Dahmer, BTK ect. A serial killer kills one victim at a time who has something in common with all his other victims, e.g all blondes, all brunettes, all children, all women, all men, all prostitutes ect.
These kids knew their killer and he knew them. Probably well. Knew their inclination to drink, party, have an open door policy at their home ect. This was no random guy hiding up in the woods and suddenly deciding to stab 4 people to death.
There is a motive behind these killings. The main motives for murder is money, sex or revenge. I would add keeping a secret but with 4 victims it is unlikely all 4 knew the killers secret. If keeping a secret known to one victim was the motive it would have been easier to get that victim alone rather than enter a house with six people or possibly more, that may or may not have been asleep. If one person in that house was awake they could have called 911. That is why I discount that theory, too many unknowns and variables.
This was not an assassination. Assassins don't use knives for a very good reason. If the target is a male and awake or wakes up during the attack the victim might fight back to the point he gains control of the assassins knife and turns it on him. If the target is a woman she might fight enough to get away. Assassins use a gun usually with a silencer and do a double tap to the head quietly and quickly.
This was a rage fueled murder. As SG described it "Sloppy, messy". No planning went into this. This was spur of the moment fueled by an overwhelming rage at one or more of the victims. You can bet the killer made a mistake or several of them that will lead to his/her arrest.
In naming the usual motives for murder, we know it was not money, nothing was stolen, it was not sex, no one was raped, so that leaves only revenge.
So what was the revenge for?
An altercation between the killer and one or more of the victims? This could have easily occurred at any one of these parties where you have testosterone filled young men drinking heavily. A friends grandson recently ended up with a broken nose after a dispute over ownership of a fishhook during a party just to outline how little a fight ending in injuries can break out where alcohol or drugs are involved. Here you have entire fraternities and sororities full of such young people all drinking and partying heavily, indeed from statistics, half of a town full. It's easy to see how an altercation that night or revenge for a prior altercation could have provoked these murders.
An ex boyfriend/girlfriend (I am not singling out any particular ex since I am sure all 4 victims have had prior ex boy/girlfriends at their age.)? Little has been said about prior relationships before college or the current ones named. M met her BF at college, E&X met at college, K had recently broken off a semi long term relationship that did not preclude a different relationship in between those on/off again breakups or even a current one that led to the breakup. Them being in a relationship does not preclude them having a fling outside the relationship at one time or another either. It's easy to see a jilted lover being responsible especially if that jilted lover believed the other three friends were in some way involved in he/she being jilted. I am not ruling out a woman with strong upper body strength, rage filled woman, with 4 drunk, sleeping victims.
Someone in that house was connected to the evil that came in it that night. That you can be sure of. Eventually the police will single out which one which in turn will lead them to the killer.
Then you have a college full of young people who live on SM and post their innermost private details of their lives on it. Nothing remains a secret for long among very socially active kids these days. Sooner or later, sworn to secrecy frat brothers or sorority sisters or not, someone will talk. After all this is the murder of 4 people, not a super secret dark of the night Greek ritual known only to the brothers and sisters of that Greek house.
Give these kids some time to think about how being charged as an accessory to 4 first degree murders can ruin their bright futures and all that sworn to be brothers and sisters forever will fly out the window.
ETA: When the killer is named there is going to be a lot of shock among relatives, townsfolk and people on here as to who it is and how close they were to the victims. IMO it's going to come out of left field.
JMO