DALLAS (CBSDFW.COM/AP) –  A grand jury is hearing evidence in the case of a former Dallas police officer who fatally shot her unarmed neighbor in his own apartment after she said she mistook it for hers.

Daryl Washington, an attorney for the family of the slain man, said the grand jury began hearing the case Monday.

Amber Guyger was arrested on a manslaughter charge after the Sept. 6 shooting of Botham Jean, a 26-year-old native of St. Lucia.

Dallas police officer Amber Guyger stands charged with manslaughter in the fatal shooting of Botham Shem Jean who she mistakenly thought was in her apartment. (CBS DFW)

Guyger, was later fired from the Dallas Police Department.

The grand jury will hear evidence and decide whether to indict Guyger.

It could also decide on a more serious charge.

Jean’s family has filed a lawsuit against Guyger and the city of Dallas in the shooting.

An online petition with 170,000 signatures, organized by local activists in late September, demanded the manslaughter charge facing the former Dallas Police officer be upgraded to murder.

Then-DA Faith Johnson had said it will be solely up to the grand jury to decide on the proper charge and manslaughter is only one of several it will consider.

“I think it’s a mini trial, evidence presented to the jury and hopefully come back with murder indictment,” Washington told CBS 11.

We know it’s rare officers are indicted in Dallas, so nothing about this can be run of the mill or ordinary,” said Lee Merritt, another attorney who is representing Jean’s family.

Jean’s mother was called before the grand jury Monday. 

A decision is expected by Wednesday.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)