IMO, it sounds like LE has their person, they are just trying to find links and motive.
http://www.foxnews.com/story/0,2933,365081,00.html
(snips)
There's obviously an issue here where the shooter wanted these girls dead and certainly carried that to its fullest extent," Oklahoma State Bureau of Investigation Inspector Stan Florence told FOX News.
We have "someone who we're interested in at this point," he said. "But we do have other leads, as well, that may lead us to other suspects."
Florence said they were acting on tips to identify the person's relationship with the grade-schoolers.
"We believe this person may have known these two girls," Florence said. "We're trying to establish the type of relationship, if there was one, where we can determine exactly what connection there was between them."
Investigators planned to hold a news conference at 3 p.m. ET to discuss the case