(CBS) — The family of a suburban woman who died in a Texas jail cell might soon learn more about her death, after arranging for a separate autopsy.

Cannon Lambert, an attorney for Sandra Bland’s family, confirmed they’ve hired their own medical examiner to conduct an autopsy, as the family does not believe the official police account that she committed suicide by hanging herself after she was arrested earlier this month.

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Bland was found dead in her jail cell on July 13, three days after she was arrested for allegedly assaulting a police officer during a traffic stop in Waller County, about 50 miles north of Houston.

Authorities have said an autopsy determined her death to be a suicide by hanging, but her family and friends have said they do not believe she would kill herself.

“We know Sandy’s spirit, her heart her demeanor,” said family friend Theresa Dear. “We know that Sandy would not commit suicide.”

In police dashcam video of Bland’s arrest, she can be heard shouting at police, accusing officers of excessive force.

“You just slammed my head into the ground. Do you not even care about that? I can’t even hear!” she said.

Bland had been pulled over for failing to signal for changing lanes. Police said she assaulted an officer during the traffic stop.

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Her family church, in Lisle, has been circulating a petition, calling for a U.S. Justice Department investigation of her death.

“I think that when you say what has happened before an investigation has been completed, you are tainting the investigation,” Rev. James Miller said.

Friends and family have said she would not take her own life, pointing to the fact she was in Texas to start a new job as a youth group outreach coordinator.

“Justice for us is the truth. We simply want to know what happened to Sandy Bland,” Dear said.

The state trooper who arrested Bland has been placed on administrative leave, pending the outcome of the investigation. The Texas Department of Public Safety has said the trooper violated procedure, but has not provided specifics.

Lambert said he was hoping to get results of the new autopsy by Tuesday. He also said he has reviewed the dashcam video of Bland’s arrest, and there appears to be no reason for police to have asked her to exit her vehicle.

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He also said the FBI is involved somehow in the investigation, but he doesn’t know to what extent.