I agree with this Ram...
I think, given all of the accounts of Kelly as having a major drug problem at the time of the murder, this business of morphine residue on drinking glasses, etc... (whether figment of addict paranoia and not really there or planted by Kelly) was probably Kelly raging herself into believing that Craig and Melissa were going to do her in - whether she wiped morphine on the glasses or it wasn't actually there. I think it's very plausible. And, for sure, if CT and MJ were f*cking one another, Kelly was in dire fear she'd lose Craig to another woman, finally. After all, she looked like the walking dead, not the vivacious fitness babe he married, and she had no career anymore... I'm sure not having an "external life" and "image" she could fall back on for comfort, she was panicking BIG TIME! She had nothing to lure him back to her with.
Consider this, too.... Kelly has to manufacture a reason to explode that rescues and diverts her from the REAL rage she feels inside toward Craig over being treated like she doesn't matter, so she concocts the deal about Melissa stealing her identity, (she knows this about MJ's history, after all, so how convenient a reason?) knowing that Craig will NOW side with her if she wants to harm her and punish her. It's the ONLY way she can turn Craig's head - the thought of having been duped or cheated - and get him away from MJ once and for all. And of course, she wants so badly for someone to be punished for all of the deep-seated hurt that Craig's cheating (and her passive acceptance of it) has caused her, but can't punish Craig for it. So instead, she projected the punishment in full on to MJ because she was afraid to actually call her husband out on it - if she did that would mean the end of her marriage, after all. That's how denial works. How could she live with finally calling her husband out on it and then NOT getting a divorce? That's what normal women do, but Kelly has never had that courage because of her own history...
{FYI ~ This is why mothers whose daughters are being molested find out and get angry AT the daughter, call her a liar, a whore, etc.. and don't go after the husband... If they were to actually face up to the fact that their husband is having sex with their daughter, there's no possible way to remain married and have the life they have as they know it. Security, comfort, wealth, etc.. would surely end.. and they'd lose absolutely EVERYTHING they held dear. The mind concocts a way to displace the anger and revulsion onto the daughter - it's very very sad and I've seen it more than once}.
Consider also... Facts state that Craig actually removed MJ from the house in good faith, for her own safety, and it was confirmed she actually did occupy the motel room, because of Kelly's rage about the two of them. Fact: It has been acknowledged that Kelly DID know about the affair. MJ was ALMOST home free - away from Kelly and any kind of revenge and that pissed her off to no end. Kelly would then have to actually DEAL with Craig over his infidelities in the house by themselves and she couldn't have that - and knew Craig wouldn't take it if it went there (usually the relationship is over for Craig if someone actually calls a spade a spade when it comes to him being f*cked up or a cheater or whatever). So, she had to figure out a way to lure MJ back to the house and have Craig support that, without looking like the one who premeditated murder or pre-arranged harm.
Answer? She would prey on Craig, intentionally, in the only way she knew how to do it... She knew that he would always defend her against someone "doing her, him or them wrong". (Remember, he would have dissociated himself with the hurt his part in the affair caused her, and an affair alone is NOT a big deal to Craig.. it's what he knows a woman should accept from him. They both dissociate themselves from their own behaviors and the impact they have on others - especially Craig). After all, countless times Craig has run to her defense, even looking like a jackass on film, flipping out in public, etc... She KNEW he would take the bait. She knew Craig just about lives and breathes to justify all of his other messed up behaviors by being "overly" protective of those he loves. It's his signature way of being.
You know, we all talk about sociopathic, evil, scumbag Craig - and he is - but the truth is, Kelly is not an angel in terms of her ability to play Craig like Craig plays her. She had a good start before meeting him, but has finely honed her own ability after having learned from the Master himself! They know exactly what one another will do for the other at all times ~ Ride or die. Their manufactured solidarity is nothing more than just f*cked up chemistry and one learning the lengths the other would go to in order to keep each of them the center of their own galaxies.
Believe me, Kelly had to know that that would be the ONLY way to get Craig back on her side (because she was so desperate to "belong" to someone and be his "one and only" and she was actually losing him this time) and to get MJ back into her physical proximity to severely punish, torture, or kill her.... (Maybe why dutiful, if not dumb, best friend Megan Foley "never noticed anything wrong" in the house prior

Yeah, because it wasn't happening and was totally fabricated!)
So back to Kelly... Rather than divorce someone who's f*cking your roommate, you muster the anger toward the "other woman" alone and corral your partner back over to your side by way of playing on his rage and inability to forgive certain things... such as stealing, hurting his wife, etc.. ("There's 3 things you don't do...." says Craig. Yeah, and Kelly knew that about him!)
For those who have been around Craig, we all know that he has a flawed sense of honor, ethics, and rules that he lives by, absolutely. Things such as someone stealing from him, someone dissing him after having been a friend, etc.. are all things that Craig cannot abide in another. And though it's really messed up because the things he gets angry over are all things he's done at one time himself to someone else, this "honor code" of his is NON-NEGOTIABLE in his mind! He is unforgiving and ruthless toward people who do those things TO him, and he is unflinching on his feelings about those things and what he is prepared to meter out if he catches someone doing him wrong! It's precisely this hypocrisy that points to all of this. She KNEW his brand of hypocrisy would win out over any possible feelings he may have developed for MJ, and his wrath would overtake his sense of pity for MJ or his need to want to help her or protect her.
Nevermind that Craig's dissociation from hurting his wife because of his OWN behavior, probably never came up very often, because that's Craig's Hypocritical Oath. He feels if he's honorable in these other areas, he can forgive himself for actually degrading a partner. But remember, direct admissions are not part of this couple's repertoire:
Blame it on a third party, and you have a neat solution because you don't have to deal
with the real problem: two f*cked up people who don't belong together and do f*cked
up things to one another and themselves.
So there's Kelly scheming, as addicts tend to do, to find a way to create ODD evidence such as an implausible mortgage report from online, various other over-obvious and planted clues, etc.. (because Craig would see these and just SNAP and not question how glaringly obvious they are) and she would NOW have her husband back - (who, by the way, admitted already to having spent part of a night WITH MJ at her motel room...). That had to burn Kelly's ASS and MJ was going to pay for it!!!
I can just see her... She was furious and created the morphine residue on glasses and identity theft evidence - really stupid things that even a common street criminal, or just anyone doing anything, wouldn't do or think to do, and had Craig believing it lock, stock and barrel. This time, sadly, I think Craig may have been duped, the more and more I think about it, into a totally manufactured homicidal rage. He was railroaded and goaded into kicking her ass and killing her, and Kelly helped, locking them forever into a pact that could not be broken! As sick as it sounds, how else can you find a way to stay connected to someone forever? Duplicity and murder.
I do think CT did the actual deed and is guilty of murder, but I am beginning to think he wouldn't have done the deed at all were it not for being manipulated into it, and MJ would be in Florida as we speak, if Kelly hadn't created a reason for him to snap on hers and their behalf. Sadly, I'll bet he doesn't even know to this day that he was pushed into reacting...
But to get out of it, consider this portrait of a 5 year old:
Craig is like a 5 year old who knocks over a lamp and breaks it and then is kicking the dog senseless when you come in to see what's happened...
"What happened here?!!" You ask.
"This dog is VERY VERY bad!! He just knocked over the lamp - I'm teaching him a lesson he'll never forget!" He says.
ALSO: This may sound odd, and I don't know how to put it but this way: Most who know Craig well enough will definitely know this, but Craig for all of his own faults and flaws, actually would see a woman he was involved with injecting drugs everyday and turning into an ugly addict, irrational, unkempt, most of all, UNSEXY, etc... he would actually HATE that and make her feel like a scumbag, even if he was doing it himself! It's just unacceptable to him... he may revile and cheat on his partner, but she has to be worthy of it, somehow. I know this sounds odd, but it's his brand of peculiarity. I don't know... I've seen really good looking women he was involved with reduced to shreds by him for the smallest of flaws, despite more glaring ones of his own. Consequently, they were probably fighting like cats and dogs and him telling her to "Clean up because it made him SICK!" because deep down Craig wanted to get clean and not live that life either. Yet, ironically, he would probably have seen Melissa as a poor addict (because she was a FRIEND and he was just fucking her, not involved with her, and a victim) that he could help get better. But it would be untolerable in his own wife for her to be the same SICK addict. I know that may not make sense to most of you, but I've seen him focus his criticisms on those close to him and NOT friends for doing the same thing! Somehow, he wouldn't hold MJ to the same standards, even if he was throwing her a bone 5x a week.
Just my two cents....