Mary O'Callaghan, a 19-year veteran, is accused of repeatedly striking 35-year-old Alesia Thomas, a handcuffed woman who refused to get into a patrol car on July 22, 2012.
"Ms. Thomas was combative. She was kicking. She was refusing to cooperate," said O'Callaghan's lawyer, Robert Rico.
Thomas later died, but the coroner was unable to determine whether Thomas' cocaine-use that day or the blows caused her death.
O'Callaghan was surrounded by colleagues and friends in the courtroom. Rico says she is a former Marine and a decorated police officer. He said he has seen the dash cam videos of the arrest and that the officer's actions were justified.
The district attorney says O'Callaghan used excessive force, kicking Thomas in the stomach and groin area and pushing her in the neck.
On Tuesday, attorneys on both sides asked for the video evidence to be sealed until O'Callaghan's trial. The judge agreed.
But Thomas' family says they want answers. They have hired Benjamin Crump, a lawyer who represented the family of shooting victim Trayvon Martin in Florida.
"We demand that the video be released to the family and the public now. The family has a right to see the video themselves," Crump said.
But the district attorney and the defense say releasing the video could prejudice potential jurors.
"We look forward to getting a fair trial with a jury that's not burdened with a video that gets spun out of control on YouTube and other sources of media," said Rico.
For the first time, we are hearing about the officer's defense. Her lawyer says while leg restraints had been placed on Thomas, they fell off. O'Callaghan had to replace them and Thomas allegedly kept kicking.
"There were numerous officers there that were attempting to take this person, not only into custody, but get her in the back seat of the police car," said Rico. "Once the video is seen, I believe that a jury will find my client not guilty."