Pima County Deputies Union Prez Initial Nancy Guthrie Team Didn't Have Much Homicide Experience

The Nancy Guthrie investigation was in trouble from the get-go because of the team's shocking lack of experience ... so says a sergeant connected to the case.

We sat down with Sergeant Aaron Cross -- the president of the Pima County Deputies Organization, a union representing sheriff's deputies -- to discuss the problems that have seemingly plagued the investigation.

Sgt. Cross notes the relative lack of experience among investigators who

jumped on the case shortly after Nancy went missing ... noting many of them had just 3 years' experience -- which isn't much when it comes to homicide.

This might explain the communication issues between detectives ... which Cross says led to lots of duplicate work -- though not necessarily gaps in the investigation.

Getty

Sgt. Cross also lifts the lid on the tension between the Pima County Sheriff's Department and the FBI ... including crediting the FBI with unearthing Ring Camera footage -- key evidence in the case.

Bottom line ... Sgt. Cross says he feels the sheriff's department hopes to solve this case from behind a desk -- which doesn't seem to think is likely.