Hall added that the officer, who has been taken into custody by the Texas Rangers, had been questioned only at the scene, where officers took blood samples to determine if drugs or alcohol were involved in the shooting.
Officials were still concealing the identity of the police officer accused of mistakenly entering a Dallas apartment on Friday and killing the Black man who lived there.
The victim was named as 26-year-old Botham Jean, who grew up in St Lucia and was an employee of accounting and consulting firm PwC.
The officer called 911 and authorities responded and took Jean to the hospital, where he was later pronounced dead.
The officer, who has not been identified, returned home in her uniform before reporting that she had shot a man.
Reporters pressed the police chief about the officer's mental state when she entered the apartment at 1210 S. Lamar St.in Dallas - was she tired, or under the influence? - but Hall didn't want to speculate.
"We're going to lift up Mr. Jean's life and the lives of others that have been killed by the Dallas police", Fullinwider said in a phone interview Friday.
"We are here to express our outrage, and we are here to demand accountability", said Imam Omar Suleiman, an activist at the event organized by the Dallas-based Mothers Against Police Brutality group.
Young King Solomon Grayson runs in front of a makeshift memorial for Jean in front of DPD headquarters. Brian Maschino
Jean attended and studied accountancy at Harding University in Arkansas.
An altercation ensued but authorities did not say how the incident escalated. "How can you make a mistake like that, getting into someone else's apartment", a resident of the apartment complex asks, speaking to Dallas News.
Jean graduated from Harding University in 2016, and he is remembered by classmates as a friendly, "all around great person" who always had a smile on his face.
Jean was listed on LinkedIn as a risk assurance experienced associate at PricewaterhouseCoopers.
"This is a bad tragedy", the company wrote on Facebook.
After entering the unit, she was confronted by a 26-year-old man.
Speaking to NBC News on the death of Botham Jean, mom, Allison Jean shared: "I couldn't believe it when we got that call".
At a Friday morning news conference, Sgt. Warren Mitchell acknowledged there are many questions about what happened that he couldn't answer.
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