Wow, what a strange 911 call. First hearing it I assumed, they were all together and got call from I and perhaps the older daughter answered her phone for her or she gave her phone to older daughter/BF because she wanted to call police herself using Dad's phone. I honestly think that mom was using "they" in a general sense; she had obviously NO idea that poor little girl was dead so why not assume "they." How old is the older daughter because if teenager, you know how dramatic they get and if I is telling the daughter what is happening, the older daughter is probably freaking out so the boyfriend started talking to I.
The ONLY clear thing to me about that 911 call is that I did NOT tell them his sister was dead and I can see that completely. He killed her, knows he had to make something up but probably couldn't quite make himself emote enough in relaying she was dead.
This is still a 12 year old boy; despite the atrocity of this crime, his emotional maturity and intellect, etc. is not developed to the point where I could see him being able to relay in a phone call authentically that his sister was butchered.
Insofar as how and why..... we truly don't know what lies beneath anyone's surface. This kid could have rage, hate, emotional issues that went deeper than anyone truly knew. We have seen this way too many times. The little I caught on the news about the pocket knife and how he was in school..... loner? bullied? possible psychological and/or intellectual disability that ran deeper. We have no clue but there was rage brewing and something triggered it that horrible day. Perhaps that poor girl caught him doing something and it was literally the straw that broke the camel's back Leila (from what I read) was a popular, smart, gregarious little girl. Was "I" the posterboard child for the exact opposite with some very deep rooted jealously towards her that finally unleashed itself with one innocent provocation by Leila.
Kids are so hard to read these days and they are so good at making parents blind. This kid was a powder keg, we've seen that way too much anymore...... so so sad