(CNN) -- [Breaking news update at 8:20 p.m. ET]
Aaron Dean, the Fort Worth officer who resigned after shooting Atatiana Jefferson dead in her home, has been arrested and charged with murder, police said.
[Previoius story, published at 7:15 p.m. ET]
The Fort Worth police officer who fatally shot Atatiana Jefferson in her home Saturday morning resigned Monday, interim Police Chief Ed Kraus said.
The officer was served a written administrative complaint Sunday, placed on detached duty and stripped of his badge and firearm, Kraus said.
"My intent was to meet with him today to terminate his employment with the Fort Worth Police Department, however, the officer tendered his resignation this morning before we met," Kraus said.
Kraus said the officer's name is Aaron Dean. If Dean had not resigned, he would have been fired for several policy violations, including the department's use of force and de-escalation policies, and unprofessional conduct, Kraus said. The officer, who was dishonorably discharged from the force, may face criminal charges, he said.
The department has presented a preliminary case to the FBI to review the officer's actions for possible civil rights violations, Kraus said.
"None of this information can ease the pain of Atatiana's family but I hope it shows the community that we take these incidents seriously," he said.
Dean was hired in August 2017 and commissioned as a licensed officer in April 2018, Kraus said.
'There is nothing that can justify what happened,' mayor says
Fort Worth Mayor Betsy Price said Monday the killing of Jefferson was unjustified.
"I'm so sorry. On behalf of the entire city of Fort Worth, I'm sorry," Price told reporters. "To Atatiana's family, it's unacceptable. There is nothing that can justify what happened on Saturday morning. Nothing."
Police responded to Jefferson's house around 2:25 a.m. Saturday after a concerned neighbor noticed her doors were open in the middle of the night.
The neighbor, James Smith, told the Fort Worth Star-Telegram he called a non-emergency police number for a safety check. He said he was worried because he knew Jefferson was at home with her nephew.
Officers searched the perimeter of Jefferson's house and saw "a person standing inside the residence near a window," Fort Worth police said.
In heavily edited body camera video released by police, Dean can be seen pointing his weapon at the window and yelling "Put your hands up! Show me your hands!" He does not identify himself as a police officer.
Two seconds later, he fired through the window.
Police said in a statement Saturday that he had "perceived a threat," and that officers provided medical care after the shooting.
Moments later, Atatiana Koquice Jefferson died in the bedroom of her own home with her 8-year-old nephew nearby.
Now Texans are outraged over the death of another black person killed at home by a white police officer.
"There was no reason for her to be murdered. None," said Lee Merritt, an attorney for Jefferson's family and the family of Botham Jean, an unarmed black man who was killed at home by an off-duty Dallas police officer. "We must have justice."
Critics slam the photo of a gun
Police said in a statement that they found a firearm when they entered the room where Jefferson died. The video released by police shows two mostly blurred clips that appeared to be from inside the home, showing a firearm.
At a Sunday news conference, a reporter asked police spokesman Lt. Brandon O'Neil if Jefferson was holding the gun when the officer shot. He declined to answer.
"There was nothing nefarious or illegal about owning a firearm, and they presented in no way that that firearm was contributory to toward the use of deadly force here," Merritt told CNN affiliate KTVT.
He said an independent law enforcement agency should take over the investigation.
"We don't think that Fort Worth Police should be investigating it on their own," Merritt said.
A doting aunt who took care of her ailing mother
Jefferson had moved into her ailing mother's home earlier this year to take care of her, Merritt said. Her mother was in the hospital on the night her daughter was shot by police.
Merritt said Jefferson graduated from Xavier University of Louisiana in 2014 with a degree in biology and worked in pharmaceutical equipment sales.
"She was very close to her family," Merritt wrote on a GoFundMe page benefiting Jefferson's family. "Her mom had recently gotten very sick, so she was home taking care of the house and loving her life. There was no reason for her to be murdered."
He said the funds collected "will go directly to funeral cost and other expenses associated with this tragedy."
Echoes of Botham Jean
Jefferson's Fort Worth house is about 30 miles west of the Dallas apartment where Jean was killed last year.
An off-duty Dallas police officer, Amber Guyger, said she mistook Jean's apartment for her own and shot him, thinking he was an intruder. Guyger was convicted of murder this month and sentenced to 10 years in prison.
Smith, the concerned neighbor who called police to Jefferson's house, said he now regrets trying to help.
"I feel guilty because had I not called the Fort Worth Police Department, my neighbor would still be alive today," he told CNN affiliate KTVT.
Community activist and pastor Michael Bell said it's a harsh reality that "you don't know if you will survive a wellness check call."
"African Americans, we have no recourse. ... This has to stop," he said.
"We're trying to obey the law, raise our families and get our kids into school, and we don't know if we're going to survive long enough to do that."