There are a number of strategies that a Criminal Defense Investigator might use to collect evidence during an investigation. They might interview witnesses, conduct background checks on those that are involved in the case (including witnesses and the alleged victim), check the facts stated in police reports, prepare legal documents, or gather witnesses that would be willing to testify in court. A Criminal Defense Investigator may also be asked to testify about an investigation themselves during a trial.

At the beginning of an investigation, a Criminal Defense Investigator must first get an understanding of the allegations against the defendant so that they know where to look when gathering evidence for the defense attorney.