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In Massachusetts prosecutors are required to give certain evidence to defendants before trial. See my earlier post Mandatory Pretrial Discovery in Massachusetts Criminal Cases.

If a prosecutor fails to disclose pertinent or exculpatory evidence, the defendant may rightfully argue that his constitutional rights (Art. 12 of the Mass. Declaration of Rights and 6th Amendment of the U.S. Constitution) were violated.

To succeed with such an argument, the defendant must show:

  1. the undisclosed evidence existed;
  2. the evidence was exculpatory;
  3. the defendant specifically requested the evidence;
  4. the prosecutor failed to provide it;
  5. and a substantial basis exists for claiming prejudice from the non-disclosure.

This standard was set forth by the Supreme Judicial Court in Commonwealth v. Bateman, 492 Mass. 404 (2023).

To prove “prejudice” from the non-disclosure of evidence, the defendant must show “there is a reasonable possibility that the nondisclosed evidence would have made a difference.” Commonwealth v. Laguer, 448 Mass. 585, 594 (2007).