Waller County Dist. Atty. Elton Mathis also announced that a panel of lawyers will help his office make decisions on the case, which could go to a grand jury as soon as next month.
Officials, who last week noted that there was marijuana in her system, said on Monday they are still awaiting more tests to determine the amount of the drug.
Bland, a 28-year-old black woman, was stopped by Trooper Brian T. Encinia, who is white, on July 10 in Prairie View, Texas. After a hostile confrontation, Bland was taken to Waller County Jail where three days later she was found dead in her cell.
According to a video from a dashboard camera in the police cruiser, Encinia told the woman he was pulling her over because she had failed to signal while changing traffic lanes.
The pair argued and it quickly escalated, with Encinia opening the driver's door and ordering Bland out of the car, and then trying to physically pull her out.
At one point Encinia points a stun gun at the woman and shouts: "I will light you up!"
Encinia was placed on desk duty after the traffic stop.
"There are many lingering questions in the Sandra Bland case," said Mathis, pledging to get answers in a "timely and appropriate manner."
As Mathis has said before, his office will look at the original arrest to determine if the trooper's actions were appropriate. Investigators will also examine Bland's death in her jail cell.
The new panel of lawyers will work alongside the district attorney's office to review the evidence and make recommendations on what to present to a grand jury, expected to meet on the case next month, Mathis said.
Last week, officials released the results of an autopsy on Bland's body, which they said showed no physical evidence of violent homicide and that the evidence was consistent with suicide by hanging.
Bland's family has insisted that she did not commit suicide. The family has said it will seek experts to do its own autopsy and forensic tests.
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