Just my two cents here, but I've looked at all the LE info, and they do not consider mom a suspect. I imagine they could tell simply from her reaction when they discovered the body of her daughter in her basement. I imagine it must have been an emotional, horrific scene. If they even had the slightest doubt about mom's involvement, they would not have cleared her so quickly.
This is a terrible, terrible case. I lurk here often and rarely post, but this one has me through and through. SL went insane, just snapped, IMO. I doubt that he and T were "romantically involved," as some have wondered here. She knew him well since she was approximately ten years old; he must have been like a secondary father figure to her, or, at the very least, completely asexual to her, being her mother's partner and her being a little girl when she first met him. Her partially clad body suggests the motive to me, as horrible as that may be. I hope I am wrong. This is heartbreaking.