Texas trooper who arrested Sandra Bland had been warned over conduct: AP

A woman carries a funeral program detailing the life of Sandra Bland following her funeral service.
A woman carries a funeral program detailing the life of Sandra Bland following her funeral service.EPA

(REUTERS) - The Texas trooper who arrested a black woman later found hanged to death in jail was warned about his "unprofessional conduct" in 2014, according to documents obtained by the Associated Press.

Sandra Bland was pulled over in her car on July 10 by a white state trooper, Brian Encinia, for failing to signal a lane change.

The discovery of the 28-year-old's body on July 13 with a trash bag around her neck provoked suspicions of racist treatment, but a senior local official said video footage indicated she was not mistreated in jail.

Bland's case follows the death of several black men in encounters with white police officers that have led to increased accusations of brutality against minorities.

The traffic stop escalated into a verbal altercation when Encinia asked Bland to put out a cigarette and she refused.

Bland was arrested and charged with assaulting an officer.

The Associated Press said it had obtained Encinia's personnel file through a public records request.

In an evaluation of his work in September and October 2014, a supervisor noted Encinia had received "written counselling for unprofessional conduct... for an incident occurring while at a school in Austin," the AP said, adding that the document provided no additional information.

The Texas Department of Public Safety could not be reached for comment on Saturday.

Encinia had been with the department for a little more than one year, and received "competent" ratings in his employee evaluations, the report said.

He has been put on desk duty while the Federal Bureau of Investigation and the Texas Rangers investigate Bland's death.

A prosecutor in Waller County, which is north-west of Houston and where the arrest and death happened, said on July 23 that an autopsy supported the medical examiner's initial ruling of suicide.

County authorities released a video of Bland at the jail to dispel rumours that she was already dead by the time records show she was booked.