Pretrial is the time period after an individual has been formally charged but before they have been convicted of a crime. During this time period, a pretrial services officer will gather information about the defendant through interviews and record checks. The pretrial services officer reports the information to the magistrate judge, so the judge can decide whether the defendant can be released on pretrial supervision or should be detained.

At a detention hearing, the judge will decide whether or not to grant pretrial release based on whether the defendant poses a risk of danger or a risk of flight. If the defendant is granted pretrial release, the pretrial services officer will supervise the defendant to mitigate any danger he or she may pose to another person or the community, to monitor that the conditions of release are being met, and to ensure the defendant attends all required court hearings.

Pretrial supervision ends if the defendant is found not guilty at trial or the charges are dropped against him or her. If the defendant is found guilty or pleads guilty, the pretrial services officer will typically continue supervising the defendant until their sentence begins. Pretrial supervision usually lasts a few months, during which time a probation officer may start the defendant's presentence investigation.