University of the Pacific grad Dawson McGehee, 27, of Manteca will serve 16 years to life in state prison for the Halloween night murder of his 56-year-old mother Katy in their home 15 months ago.Manteca Police arrested Dawson McGehee driving on nearby Lathrop Road within hours after Katy’s body was discovered near the doorway with defensive knife wounds to her arms and hands and with her car keys held tightly in her grasp. The McGehees lived in their northwest corner of Manteca, east of Union Road and north of Lathrop Road.Defense attorney Public Defender Katy Garrigan had used insanity as a defense in the case but a jury ruled against her attempt to prove that McGehee was not of sound mind when he killed his mother in October of 2011. She said she doubted he would ever be released from prison.