CSI has located the mother of Gil Grissom.

Tony Award-winner Phyllis Frelich has landed this key role and will appear in an episode tentatively scheduled for February 3.

Here's a rundown of what's on tap:

A murder will take place at a school for the deaf where the elder Mrs. Grissom is a teacher. She'll butt heads with Sara when that Mrs. Grissom shows up to investigate.

This episode will also feature Marlee Matlin - who we speculated could take on the role of Grissom's mother - as a school colleague who used to date Gil.

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