McCullough insists that he's innocent of the crime, and certain members of his family and his defense attorney back him up. Among the alleged holes in the case is a lack of forensic evidence tying him to the crime. Ridulph's doll, which was handled by the killer and recovered hours after the search for the child began, has long since been lost, taking with it the potential for any DNA or fingerprint evidence. His mother's confession has also been called into question, and is impossible to verify since she is long since deceased. The defense also claims that his sister Janet's apparent hatred for Tessier is motive for her to want to see him behind bars. McCullough insists that the photo lineup given to Kathy Sigman was intentionally skewed to get her to select his image over the other men shown, since their pictures were all relatively similar in appearance and his was somewhat different. Some experts also point to the fallibility of eyewitness testimony and jailhouse informants, who often are looking for some type of leniency in exchange for cooperation [sources: O'Neill, Goode].
Although many crime procedural shows (and apparently McCullough's defense) would have us believe that DNA and forensic evidence are the most common catalysts for cold case convictions, at least one scientific study shows otherwise. Published in the Journal of Forensic Sciences in 2014, the study found that, of the cold cases researchers examined, a mere 3 percent of cases were solved using DNA or other forensic evidence, as compared with 63 percent of cases involving testimony of new witnesses [sources: Vergano, Davis et al..]. In this case, Tessier/McCullough's mother provided new witness information that changed the scope of the original investigation, and the prosecution gathered enough other evidence to adequately prove his guilt, at least in the opinion of the presiding judge.
Plus, it's not exactly new territory for an accused/convicted criminal to claim they're being wrongfully targeted. Just ask anyone who believed serial killer Ted Bundy when he maintained his innocence, only for him to eventually confess to at least 30 murders [sources: Pinsky, Bergeron].