Video shows arrest of woman found hanging in jail

Last Updated Jul 17, 2015 8:32 PM EDT

Amateur cell phone video shot by an unknown bystander allegedly shows Waller County police officers subduing 28-year-old Sandra Bland, the woman whose death in a Texas jail is currently being investigated, reports CBS News Houston affiliate KHOU's Sherry Williams.

"You just slammed my head into the ground, you do not care about that. I can't even hear," Bland said in the video.

On July 10, an officer stopped Bland for not signaling during a lane change in Waller County, Texas, 50 miles northwest of Houston. The Chicago-area native was in Texas to start a new job.

Bland was arrested for assaulting the officer. Three days later she was found hanging in her jail cell.

The medical examiner ruled the death a suicide, but Bland's family said she would never have taken her own life.

"It is unimaginable, and difficult to wrap our minds around the Sandy that we knew, for this to be characteristic of her," her sister Sharon Cooper said.

While the family said she was not diagnosed with clinical depression, she did talk about emotional issues in a March video posted on social media.

"I have to be honest with you guys, I am suffering from something that some of you all may be dealing with... it is a little bit of depression as well as PTSD," she said.

In Texas, Waller County District Attorney Elton Mathis said the Texas Rangers will lead an investigation. The FBI said Friday it would be monitoring the case as well.

"I will be taking this to the Grand Jury of Waller County so the public can have the final say on this issue," Mathis said.

The state trooper who stopped Bland was placed on administrative leave pending the outcome of the investigation. According to the Texas Department of Public Safety, the trooper violated procedure, though the specifics of how are "still being determined," according to agency spokesman Tom Vinger.

Bland's friends described her as a civil rights activist. She posted videos related to the "Black Lives Matter" movement on Facebook.