The case against a white Dallas police officer who shot and killed a black neighbour in the neighbour's apartment will be presented to a grand jury, which could decide on more serious charges than manslaughter, the district attorney overseeing the case said Monday.

Lawyers for the victim's family questioned why it took three days for officer Amber Guyger to be charged and why she was so quick to use deadly force in her encounter with 26-year-old Botham Jean, who lived on a different floor in the same apartment complex. She told authorities she mistook the neighbour's unit for her own.

Guyger was booked into the Kaufman County Jail after being taken into custody Sunday, the Texas Department of Public Safety said in a news release. The department said the investigation in the off-duty shooting is ongoing and that no additional information was available.

A jail employee said Guyger was released on bond. Online records initially showed she was in custody, but she later was not listed on the jail inmate roster.

Guyger fatally shot Botham Jean, 26, on Thursday at Jean's apartment.

Botham Jean, 26, lived in the apartment directly above Guyger. (Jeff Montgomery/Harding University via AP)

Lawyers for Jean's family had been calling for Guyger's arrest, saying the fact that she had remained free days after the shooting showed she was receiving favourable treatment. They held a news conference Sunday night, shortly before the arrest was announced, making another plea for the officer to be taken into custody and saying their team had presented new evidence — a witness and video footage — to prosecutors. They didn't provide details.

The family lawyers weren't available for comment after the arrest came.

On Saturday, one of the lawyers, S. Lee Merritt, said the man's loved ones weren't calling on authorities to jump to conclusions or to deny Guyger her right to due process. But he said they wanted Guyger "to be treated like every other citizen, and where there is evidence that they've committed a crime, that there's a warrant to be issued and an arrest to be made."

'First step' toward justice

The group Mothers Against Police Brutality said the arrest is a "first step" toward justice and accountability but should have come sooner. Co-founder Sara Mokuria said the group expects transparency in the case going forward.

Dallas Mayor Mike Rawlings tweeted a statement Sunday night, thanking investigators and asking for continued prayers for Jean's family. He said he appreciated that citizens and community leaders "were so respectful of the investigative process over these past few days."

My statement on tonight’s arrest of Amber Guyger <a href="https://t.co/pIfToTpSsN">pic.twitter.com/pIfToTpSsN</a> —@Mike_Rawlings

Police Chief U. Renee Hall said the day after the shooting, her department was seeking manslaughter charges against Guyger, 30, a four-year veteran of the police force. But Hall said Saturday that the Texas Rangers, who have taken over the investigation, asked her department to hold off because they had learned new information and wanted to investigate further before a warrant was issued.

It was unclear if Guyger had legal representation. She could not be reached early Sunday for comment.

If it was a white man, would it have been different? Would she have reacted differently? - Allison Jean, victim's mother

Meanwhile, Jean's family also hired lawyer Benjamin Crump, who is best known for representing the families of Trayvon Martin and Michael Brown.

According to police, Guyger shot and killed Jean after returning in uniform to the South Side Flats, where they both had apartments, following her shift. She reported the shooting to dispatchers and told officers who responded that she had mistaken Jean's apartment for her own.

Many questions remain about what led her to shoot Jean. Hall said the officer's blood was drawn at the scene so that it could be tested for alcohol and drugs. Investigators haven't released the results of those tests.

Race issue

Jean's mother, Allison Jean, wondered whether race could have been a factor. Her son grew up in the Caribbean island nation of St. Lucia before attending college in Arkansas.

"If it was a white man, would it have been different? Would she have reacted differently?" Allison Jean said Friday.

Jean wasn't the first person shot by Guyger. She shot another man, Uvaldo Perez, on May 12, 2017, while on duty.

According to an affidavit in the case filed against Perez, police were looking for a suspect when Guyger and another officer were called to assist a third officer. Perez got out of a car and became combative with Guyger and another officer. A struggle began and Guyger fired her Taser at Perez, who then wrested it away from her. She then drew her gun and fired, wounding Perez in the abdomen.

Guyger was not charged in the 2017 shooting.

Police association weighs in

Sgt. Mike Mata, president of Dallas's largest police employee organization, the Dallas Police Association, on Saturday called for an "open, transparent and full investigation of the event," the Dallas Morning News reported. He described Jean as an "amazing individual" and said that "if the grand jury deems necessary, this officer should have to answer for her actions in a court of law in Dallas County."

Allison Jean and her son Grant, 15, mourn Botham Jean, Allison's son and Grant's brother, during a prayer service at the Dallas West Church of Christ on Sunday. (Shaban Athuman/Dallas Morning News/Associated Press)

Friends and family gathered Saturday at the Dallas West Church of Christ to remember Jean, who had been working for accounting firm PwC since graduating in 2016 from Harding University in Arkansas, where he often led campus religious services as a student. They described Jean as a devout Christian and a talented singer.

"Botham did everything with passion," Allison Jean told the prayer service. "God gave me an angel."

His uncle, Ignatius Jean, said the killing has devastated the family and left it searching for answers.

"You want to think it's fiction ... and you have to grapple with the reality," he said.

With files from Reuters