A policewoman mistakenly entered the wrong apartment and shot dead a black man who lived there, officials in Dallas have said.
The officer, who has not been identified, thought she was walking into her own home.
Police intend to charge the woman with manslaughter, and she has been placed on leave in the meantime.
The killing has sparked protests in Texas with demonstrators calling for the policewoman to be jailed immediately.
Crowds also gathered for a candlelight vigil for the victim, identified as 26-year-old Botham Shem Jean, who moved to the US from Saint Lucia in the Caribbean.
Imam Omar Suleiman, an activist who attended demonstrations organised by the group Mothers Against Police Brutality, questioned why the officer was not being held.
"We are here to express our outrage, and we are here to demand accountability," he said. "If this was not an officer that pulled the trigger, this person would be in a jail cell tonight."
Others carried placards emblazoned with the words: "Where is justice when police kill us?"
Speaking at a news conference, Dallas police chief U Renee Hall said the shooting was "a very unique situation" and that officers had "ceased handling [the incident] under our normal officer-involved shooting protocol".
Officials added that the officer in question was being tested for drugs and alcohol.
Police are still determining what interaction took place between the female officer and Mr Jean. However, the officer did call emergency services after shooting the man, telling them she thought she had entered her own apartment.
Chief Hall said: "Right now there are more questions than answers."
Speaking about her son, who worked at the accounting firm PricewaterhouseCoopers in Dallas, Allison Jean said her life had become a "nightmare".
"I wish I would wake up and find that it wasn't true," she told NBC News, adding that the circumstances surrounding Mr Jean's death made no sense.
She said he "was in no wrong place at any wrong time", describing the flat as her son's "sanctuary".
"He didn't deserve this," she added.