Which official is responsible for conducting presentence investigation in most jurisdictions?

Answer 1

It may be done differently, by different units, in different jurisdictions, but the ones I am familiar with are conducted by a special unit of the Sheriff's Office assigned to the Circuit Court specifically to perform these duties. In other jurisdictions I am familiar with a group of special investigators working for the Prosecutor's Office handles them.

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In the State of Missouri the Dept. of Proation and Parole conducts the investigation for all counties in the State.

Answer 2

Depends on the jurisdiction you are asking about. It can be done by a unit of investigators from the local law enforcement agency, or a group of investigators assigned to the court prosecutor's offices.

Answer 3

The probation department is responsible in most jurisdictions.

Added: Rather than "most" I would probably say SOME. In other jurisdictions, the Sheriff's Dept., or the Prosecutor's Office, or even the Court itself, maintains a staff of investigators who have this responsibility.