A white policewoman who gunned down a black accountant in Texas has been identified as new video emerges of the frantic moments after the officer mistakenly entered his home thinking it was hers and opened fire.

Amber Guyger, 30, was identified as the off-duty officer who shot 26-year-old Botham Jean in an apartment block in south Dallas on Thursday night.

Instagram footage posted by a neighbor shows a female uniformed officer crying into her phone on a walkway of the apartment block. She is heard screaming 'oh God!' into the phone before she dashes away out of view.

Moments later, the victim is pulled past on a gurney as medics desperately try to revive him. Four officers follow directly behind and another runs to catch up.

Dallas police on Saturday revealed Guyger had worked for Dallas Police Department for four years on the Southeast Patrol Division.

Dallas police initially said they would seek her arrest but then handed the case over to the Texas Rangers in order for an unbiased investigation. The Texas Rangers postponed seeking a warrant for manslaughter charges, saying they needed more time to investigate information that had only recently emerged following their interview with the officer.

Dallas Police Officer Amber Guyger was identified as the off-duty officer who shot 26-year-old Botham Jean in an apartment block in south Dallas on Thursday night

New footage from the aftermath of the deadly shooting of 26-year-old Botham Jean by a female cop on Thursday shows a police woman crying into her phone after the incident

After the woman police officer walks away, medics come by with Jean on a trolley as they frantically try to revive him

'She is devastated,' a Dallas police officer close to Guyger told Dallas News. 'She is so, so sorry for this family.'

Guyger, the sole woman on a elite crime response team of 10 officers who make high-risk arrests, shot another man in 2017, this time a suspect who had taken her Taser.

Uvaldo Perez, 47, was hit once in the abdomen, but survived and was sentenced to two years on drugs charges. Guyger was not indicted over that shooting.

The policewoman moved into the South Side Flats about a month ago but had never met Jean. According to police, she returned home in her uniform after a shift and then called dispatch to say she had shot a man.

She later told the officers who responded that she believed the victim's apartment was her own when she entered.

The responding officers administered first aid to Jean, a native of the Caribbean island country of St Lucia who attended Harding University in Arkansas and worked for accounting and consulting firm PwC. Jean was taken to a hospital, where he died.

Guyger has been tested for drugs and alcohol but results are not immediately available, according to Police Chief Renee Hall.

Hall declined to speculate as to whether fatigue or other factors, including race, may have factored into the shooting.

She also said the Texas Rangers will conduct an independent investigation. A warrant for Guyger's arrest has not been issued because the Rangers wanted to examine new information first.

'Right now, there are more questions than we have answers,' Hall told a news conference. She said she spoke to Jean's sister to express the department's condolences to the family.

The block of flats is just a few streets from Dallas police headquarters.

Jean grew up on the Caribbean Island of St Lucia and studied at Harding University in Arkansas. He is seen above in a Facebook photo

Officials believe Guyger was confronted by Jean, who pulled her gun on him and fired. He is pictured in a Facebook photo, left, and leading a college service on September 21, 2017

Residents of the building said they can access their units with a key or through a keypad code.

Jeffrey Scherzer, who lives at the complex, said when he returned home late at night an officer escorted him to his flat and warned him to steer clear of a blood trail.

Jean's mother, Allison, suggested in an interview on Friday that her son might still be alive if he was white.

'I didn't know she was white until now. If it was a white man would it have been different? Would she have reacted differently?' she told KXAS.

Allison, who has held government posts in St. Lucia, where she lives and where her son grew up, said her son's death 'just feels like a nightmare.'

State Senator Royce West also raised the racial aspect of the shooting, telling a press conference on Saturday: 'Is this a white on black crime? Yes,' he said, according to the Star-Telegram.

'It was a white, female Dallas police officer who shot and killed a person from St. Lucia of African descent.

'Is this a race-related crime? Don't know. I would hold any type of decision you make on what happened until all of the facts come in.'

West said Guyger entered the apartment through an open door: 'We need to find out whether there was a personal relationship,' he said. 'There are so many facts that need to be looked at before determining what kind of homicide this is.'

Jean was remembered as a devout Christian who regularly led worship when he was at Harding University, a private Christian institution

Jean graduated from Harding University in 2016, and is pictured speaking speaking there in 2014

The island country's government issued a statement Friday expressing 'shock' at the killing and extending condolences to the Jean family. It said officials at its embassy in the US would provide assistance to the family.

Harding University said on Friday Jean often led campus worship services while he was a student.

Family and friends described Jean as a devout Christian and a talented singer. His uncle Ignatius Jean said the slaying left relatives devastated and looking for answers.

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

Jean's sister, Allisa Charles-Findley, said she needs 'answers for my baby brother.'

'Just last week I was thinking of what to get you for your birthday,' she wrote on Facebook, 'now I have to go pick out your casket.'

Officer Guyger said she mistakenly walked into Jean's apartment (pictured on Thursday from the street) thinking it was her own

The shooting happened just before 10pm Thursday at the South Side Flats in south Dallas

Neighbor Alyssa Kinsey told The Dallas Morning News that Jean helped her move new furniture into her apartment soon after she moved into the building with her family in April.

'I'll remember his smile,' she said. 'It just lit up a room.'

Nathan Monan, a friend from Harding University, said Botham Jean was kind to everybody and would often lead people in song during chapel.

'He lived what he spoke,' Monan said, adding that Jean's death has stirred emotions of overwhelming sadness and anger. 'This doesn't make sense to anybody right now.'

A YouTube video posted in 2014 shows Jean making his pitch to become the university's student association president.

'I want to serve,' he says in the video. 'My Harding experience has really inspired me to want to serve and I want every student at Harding to have the best Harding experience possible.'