Now, nearly four years after [Breonna] Taylor’s killing, federal officials are taking the extraordinary step of placing [former officer Brett] Hankison before a jury for a third time. The move points to polarizing questions regarding what amounts to justice in the killing of a Black woman during a raid at her home that helped spark nationwide social justice protests. Among those questions: whether the federal government’s push for accountability will be achieved by trying to convict this former officer...

On the night Taylor was killed, Hankison was among seven officers serving a warrant in the drug investigation. Awakened as police forced entry to her apartment, [Taylor's boyfriend Kenneth] Walker fired a warning shot from a legally owned handgun that struck officer John Mattingly in the thigh.

Mattingly and another officer, Myles Cosgrove, returned fire, killing Taylor. Prosecutors said Hankison retreated outside the apartment complex and blindly fired through a window and door, both covered by shades and curtains...

Hankison, who testified both times, told jurors he heard gunfire from what he mistakenly believed was a semiautomatic rifle, and he started shooting because he thought fellow officers were at risk of being killed.