PHOTOS: Sandra Bland investigation
Sandra Bland died in her Waller County jail cell July 13, three days after a confrontation with the white officer. Authorities say she committed suicide.
On Aug. 4, Bland's mother sued the state police agency, Trooper Brian Encinia, Waller County and two jail employees.
The Texas Attorney General's office Tuesday asked U.S. District Judge David Hittner to dismiss the complaint, arguing the police agency has constitutionally protected immunity and Encinia has qualified immunity. State lawyers also contend the lawsuit raises vague and insufficient allegations of civil rights violations.