A grand jury in Texas has indicted a white former Dallas police officer for murder over the killing of her unarmed black neighbour after she allegedly mistakenly entered his apartment and shot him.

Key points: The family of Ms Guyger's alleged victim is suing her and the city of Dallas

The family of Ms Guyger's alleged victim is suing her and the city of Dallas Mr Jean's family says she used excessive force and was not properly trained

Mr Jean's family says she used excessive force and was not properly trained The original charge of manslaughter had been criticised as too lenient

Amber Guyger was arrested on a manslaughter charge three days after the September 6 shooting of her 26-year-old neighbour Botham Jean, a native of the Caribbean island nation of St Lucia who attended college in Arkansas and had been working in Dallas.

Ms Guyger told investigators that after finishing her shift, she returned home in uniform and parked on the fourth floor of her apartment complex's garage, rather than the third floor where her unit was located, according to an affidavit prepared by the Texas Rangers.

She said she reached what she thought was her apartment — Mr Jean's was directly above hers — and found the door ajar.

She opened it to find a figure standing in the darkness and said she pulled her gun and fired twice after the person ignored her commands.

The former police officer who shot Mr Jean was initially charged with manslaughter. ( AP: Shaban Athuman )

Ms Guyger has been fired from the department and Mr Jean's family has filed a lawsuit against her and the city of Dallas.

The federal suit argues Ms Guyger used excessive force in the shooting and contends the department did not give her adequate training.

The circumstances of the shooting sparked outrage and led many to question Ms Gugyer's account of what happened.

Critics, including Mr Jean's family, also wondered why it took three days for Ms Guyger to be charged, why she wasn't taken into custody immediately after the shooting and whether race played a factor in her decision to use deadly force.

Responding to criticism that the original manslaughter charge was too lenient, Dallas County District Attorney Faith Johnson said the grand jury could decide on the more serious charge of murder, which it did on Friday (local time).

Mr Jean's killing thrust Dallas into the national conversation on the intersection of race and law enforcement, a dialogue revived by the high-profile trials of officers charged with murder in police shootings.

In October, white Chicago officer Jason Van Dyke was found guilty of second-degree murder over the 2014 on-duty shooting of black teenager Laquan McDonald. Van Dyke shot McDonald 16 times.

And in August, white former Dallas-area officer Roy Oliver was convicted of murder after firing into a car filled with black teenagers leaving a house party in 2017 and fatally shooting 15-year-old Jordan Edwards.

ABC/AP