KBI stands for the Kansas Bureau Of Investigation. In the novel In Cold Blood, Truman Capote details the 1959 murders of four members of the Clutter family (Herb, Bonnie, Nancy, and Kenyon) in Holcomb, Kansas. The killers are Perry Smith and Dick Hickok, both on parole at the time of the murders; accordingly, Dick's last cellmate in prison, Floyd Wells, who was a former Clutter farm hand, had unwittingly informed Dick that it sometimes cost Herb Clutter ten thousand dollars a week to keep his farm running.
Based on the information, both Perry and Dick drive from Olathe to River Valley Farm in Holcomb, where the family lives. They murder the Clutter family in cold blood despite being unsuccessful in uncovering the fabled ten thousand dollars at the Clutter residence. After committing the murders, both men flee the scene without leaving a trace of their presence.
In the story, Alvin Dewey and his team of investigators from the Kansas Bureau of Investigation (KBI) proceed to interview anyone remotely connected to the Clutters in a bid to discover the identity of the murderers. Eventually, Dewey is able to interview Dick's ex-cellmate, Floyd Wells.
When Dewey later shows his wife, Marie, dossiers with photographs of the two murderers, it is noted that Dick Hickok's KBI number is 97 093. He also has an FBI (Federal Bureau Of Investgation) number 859 273 A. The FBI and KBI store fingerprint and criminal records of felons in their file systems. Local law enforcement agencies can request to see the criminal records of certain felons if KBI or FBI numbers are available to them.