Crime scene staging is done by a perpetrator to cover up the original crime. The goal is to avoid arrest, to get control of the investigation, and confuse and distract LE and the public. It is basically a hoax to cover up a crime.
I am not sure what the FBI agent had in mind, but for example, this could have been a robbery gone wrong, resulting in the death of the homeowner. The robbers decide to cover their tracks and pretend a kidnapping had taken place. This serves to scatter the police looking for the homeowner and kidnappers. LE typically then does not do a great job securing the crime scene, or examining the home for evidence. They use their resources out in the community searching for a victim who may still be alive. They are thinking kidnapping, not death during a robbery.
The ransom notes could just be part of the staging, or an attempt to make a big pay day off the death.
Same situation if someone killed NG in or outside the home. Stage it like a kidnapping.