Could tire tracks help crack Nancy Guthrie case — and is the FBI building a suspect profile? Day 67

The initial assumption by the Pima County Sheriff's Department that Nancy Guthrie was a 'walk-away' led to a failure to treat the scene as a serious crime from the outset. This likely resulted in the destruction of critical evidence, such as shoe and tire impressions, as first responders and media entered the property without strict crime scene protocols. Retired FBI agent Maureen O'Connell explains that proper crime scene management involves creating separate access paths and carefully preserving all potential evidence, which was not done here.

The host's source indicated the 'walk-away' theory was pursued for 'much longer than expected' (08:53). O'Connell states, 'once you say this is a crime scene, it's almost too late because...shoe impressions are destroyed, tire impressions are probably destroyed' (11:48).

Despite the FBI's involvement, a suspect profile for Nancy Guthrie has not been released. Maureen O'Connell highlights that the FBI's Behavioral Analysis Unit typically creates and releases such profiles, even when a suspect is unknown, to guide public awareness and aid the investigation. She argues that the FBI possesses unique, comprehensive information from witness interviews and scene processing that could form a highly effective profile, and their failure to do so is a significant omission.

O'Connell states, 'The FBI needs to pull out a put out a profile like they've done for hundreds and hundreds of other cases' (33:21) and questions, 'Why aren't they doing that?' (33:38).

Tire prints can be valuable evidence, especially when looking for a specific vehicle. The FBI maintains an extensive database of tire impressions. Even on challenging surfaces like decomposed granite, oblique lighting and specialized photography with scales can capture ridge details. However, while a tire print can help identify a vehicle's make and model, it's not typically a starting point for identifying an unknown suspect directly, unless combined with other intelligence or used to verify a suspect's vehicle.

O'Connell describes the FBI's 'database filled with every tire impression you can imagine' (20:10) and the use of 'oblique lighting and a really good photographer' (21:26) for difficult surfaces. She notes that a tire print is 'much better when you're looking for a vehicle' (22:56) rather than an unknown person.

Even if a scene appears 'clean' with no visible signs of assault, forensic investigators can still find crucial evidence. Techniques like luminol can reveal hidden blood spatter, and careful examination of disturbed items (e.g., a bedspread) can uncover DNA or other traces. O'Connell hypothesizes that if Nancy Guthrie was subdued quickly, blood might have been absorbed by a pillow and then concealed by a flipped blanket, requiring meticulous investigation to uncover.

O'Connell explains using 'luminol and smaller sections' (26:20) and 'black light on carpeting' (26:35) for invisible blood. She describes a scenario where blood on a pillow could be hidden by a blanket, requiring an investigator to 'unflip it' (28:39) to find evidence.