I don't think he physically can be, he should have an alibi.Alright let's do a little theory about our mysterious killer and i'm interested on hearing what you think about it. I did share my theory previously of some suspects i thought about involving Zach, Ethan and Brooke but did anyone else got this vibe that John (Erynn's and Iris's dad) might be our guy. I mean what do we know so far about John? He does seams cool, willing to help Erynn regarding her situation and was more than cool back in the days when MC dated Iris. When Melissa described her ex John was a perfect match. Now why do i think he might be our guy. Well first of all i think it was Layla mentioning that "another girl is found dead". That another means there were others as well meaning Rachel wasn't first victim but one of who knows how many and for how many years. Age for John is good if we presume that he has done that before. I presume from late teens into adulthood meaning from 17-25 years. I presume now that he's in his 40s something. After that we have Iris. Now unless i missed something but where is Iris's mom? Next is John and Iris are in MCs hometown (i'm guilty, i forgot the name) for a month and soon afterwards we have Rachel dead. Some of you might say its coincidence but i think something might happening here that involves John.
When you have the scuffle with Ethan, there's 2 possible characters that can come to your rescue, John or Valeria.
In the John scenario he helps you knock some teeth in, then you go and spend some time with him in a bar where you tell him the whole story of Ethan and Erynn(including a fade to black time jump).
Basically he was spending time with the MC at what should be Rachel's time of death.
In the Val scenario, he's "somewhere", still having different killers depending on wether you are dating Val sounds really out there, not a good use of the butterfly effect that this game pulls off rather well honestly.
I do have a soft spot for the guy, since he seems like the only nice guy around...