From the article Kimster linked above.............. (underline mine)
Steve Brown, now a private investigator working for Haleigh's mother, Crystal Sheffield, said he believes the Putnam County Sheriff's Office knows who is responsible for Haleigh's disappearance."There may be other people culpable, but as to who killed Haleigh, that's not going to be a big surprise," Brown said.
From the sound of that, it would narrow the field down to two people. Another report states that MC would exchange what she knows and testify for a reduced sentence on the drug charges. If that's accurate, that leaves only one person.