Aaron Dean is the first law enforcement officer to face a murder charge in Tarrant County for an on-the-job shooting.

The case against the former Fort Worth police officer who shot and killed a woman in her home is now in the hands of the Tarrant County District Attorney. District Attorney Sharen Wilson says her office will prosecute ex-cop Aaron Dean to the fullest extent of the law in the killing of Atatiana Jefferson.

Dean is the first law enforcement officer to face a murder charge in Tarrant County for an on-the-job shooting, according to a spokeswoman for the district attorney's office.

On October 12, Dean and his partner responded to a call from a neighbor concerned that the door at Jefferson's mother's home in east Fort Worth was open in the middle of the night. Video recorded by Dean's body camera shows him quietly checking the perimeter of the house, peering into windows, and entering the backyard through a gate in the fence. When he saw Jefferson standing in a back bedroom window, he shouted for her to raise her hands and shot her through the glass. He never identified himself as an officer.

Jefferson and her 8-year-old nephew were up late that night playing video games. Her nephew was in the room when she was shot, according to a police affidavit. Dean resigned from the force two days later and was arrested by Fort Wort police for murder. He's out on bond.

Jefferson, 28, worked selling pharmaceutical equipment and was studying for the medical school entrance exam. She'd moved in with her mother, who'd been unwell, to help out.

Now, prosecutors will present the case to a Tarrant County grand jury. On Friday, Wilson announced that her office will seek an indictment for murder against Dean.

What is a grand jury?

Every felony case is presented to a grand jury, which is made up of 12 citizens who hear the facts of the case from a prosecutor, and make a determination of whether there's probable cause that a crime was committed. Under Texas law, prosecutors have 180 days to present the case to the grand jury, since Dean is out on bond and no longer in custody.

A grand jury does not determine guilt or innocence, but their decision to indict or not determines whether a case can move forward or not. A grand jury can also choose to indict on a different charge than the one prosecutors are seeking.

"They don't make their determination based on whether the DA's office can prove its case, it's just whether the police had probable cause at the time of the arrest," says Jade Mens, a former Tarrant County prosecutor who is now a private defense attorney.

In Texas, grand jurors are drawn from driver's license holders. Tarrant County has two grand juries at a time, each for three months at a time.

How does the grand jury work?

Prosecutors present evidence in closed proceedings to help the grand jury make its decision. Defense attorneys are not allowed to present in person to the grand jury or sit in on the presentations, though they can give the grand jury some limited information, like a notarized statement from a witness.

Prosecutors can call witnesses, but don't always do so, says Sherry Armstrong, an attorney who worked as a Tarrant County prosecutor for 14 years. The grand jury can ask questions of both witnesses and prosecutors.

The proceedings are not open to the public, and the grand jury's deliberations are done in secret.

What's the timeline for the grand jury?

Usually, once prosecutors take over things slow down. By law, the district attorney has up to six months to present a case to a grand jury. This six-month window gives prosecutors enough time to do more investigating, if necessary, and wait for any reports from crime labs or medical examiner documents that they may need to present to the grand jury. Armstrong says it's not always necessary to wait, since some cases come from police detectives with ample evidence to present.

Armstrong says with Dean’s case, prosecutors may move quickly.

"In this case there's not a lot of witnesses, so it may not take as long," she says. "And if they don't have a lot to present, it could be a one day, few hour presentation, and grand jurors could meet and vote that day."

How hard is it for prosecutors to get an indictment?

"I think it's easier to get an indictment if they want it, because it's all in the way you present it," Armstrong says.

The decision to indict or not is up to the grand jury, and the prosecutor’s job is to present all the facts so they can make the best decision, but persuasion is part of a prosecutor's job.

Prosecutors make strategic decisions in presenting a case.

Grand juries develop different "personalities" over the course of the three-month term, so a prosecutor may choose to pick the grand jury they think will be more receptive to the facts of the case, Mens says. In a diverse county like Tarrant County, the grand jury brings in a range of perspectives.

"Sometimes grand juries are rogue. They have people who feel very strongly against whatever that position is and it can be a tough sell," Mens says.

If a grand jury is newly empaneled, the prosecutor may wait until its preferences and peculiarities are clearer before presenting a complicated or sensitive case.

That all has some effect, but Mens and Armstrong both say a prosecutor's influence is still limited.

"People need to understand that the police can do so much, the DA's office can do so much," Mens says. "But at the end of the day, because of the way the grand jury process is set up, it's their vote. So whether this goes on or whether this stops here, it's on them."

Who will prosecute the case?

The Tarrant County District Attorney hasn't yet publicly named the prosecutor in her office who will try the case.

The office has a specialized team to handle criminal cases against law enforcement officers. And Mens says it would be a shock if the district attorney didn't assign the case to that team: the Law Enforcement Incident unit.

"These prosecutors have been trained extensively on the proper responses from police, the protocols that are supposed to be followed, as well as the opposite of that, like what wasn't reasonable in this scenario, what should have happened but didn't happen," she says.

The Law Enforcement Incident unit is handling another case where a police officer is facing charges for killing someone – former Arlington officer Bau Tran, who shot and killed O'Shae Terry last year during a traffic stop. A Tarrant County grand jury indicted Tran for criminally negligent homicide.

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