Black Lives Matter activists deserve credit for the prosecution of Kimberly Potter, the former Minnesota police officer who was convicted of manslaughter for the death of Daunte Wright, an unarmed Black man killed during a traffic stop. They should be wary, however, of the hardcore strategies prosecutors deployed to win their case. "Lawful but awful" is not the ultimate route to racial justice.

The Potter case illuminates a tension at the heart of the Black Lives Matter movement: It wants to reduce the power of prosecutors and undo harsh sentencing regimes that have helped to create mass incarceration and vast racial disparities in the US criminal legal system, even as it demands that prosecutors use that system to hold police officers accountable for misconduct.

At trial, Potter testified that the only reason she pulled over Wright was that she was training a rookie officer who noticed that Wright's car had an air freshener hanging from the rearview mirror and that its registration was expired. Potter, who had been a cop for 26 years, admitted that ordinarily she would not have stopped someone for such minor infractions during the height of the pandemic.

A records check revealed that Wright, 20, had an outstanding warrant for a gross misdemeanour gun charge. As the officers tried to arrest him, Wright returned to his car and Potter said she believed he was trying to flee. She withdrew her gun, shouted "Taser" and shot him in the chest. Potter claimed that she mistook her gun for a Taser and had not intended to kill Wright.

This happened just miles away from the Hennepin County courthouse, where, in one of the most high-profile trials in decades, Derek Chauvin, another White former police officer, was being prosecuted for the murder of George Floyd. Black Lives Matter activists protested, days and nights of demonstrations ensued — and, in near-record time for a police-involved shooting, Potter resigned from the police force and was criminally charged in Wright's death.

Activists obtained the prosecution they agitated for, but winning a conviction represented a huge challenge for the Minnesota attorney-general's office. Most police officers who mistake their gun for a Taser don't even get prosecuted. And Potter, who testified that before that day she had never fired either weapon in the line of duty, was a far more sympathetic defendant than Chauvin. The defence presented officers, some of whom were Black, who testified that Potter was justified in using either her Taser or her gun under the circumstances.

To convict Potter of first-degree manslaughter, which carries a sentence of up to 15 years, prosecutors had to prove only that Potter committed a misdemeanour — recklessly handling a firearm — that caused Wright's death. This is the manslaughter version of the felony murder charge that prosecutors used to convict Chauvin.

Prosecutors often rely on these kinds of charges when they want the most severe punishment for people who have killed accidentally. But the charges are controversial because people get locked up for homicide when the underlying crime they committed was significantly less harmful. Felony murder and "misdemeanour manslaughter" operate to make it easier for prosecutors to win cases. The United States might have inherited the felony murder rule from England, which abolished it in 1957 because of its potential for unfairness.

Potter’s conviction was also advanced by another extreme prosecutorial power — this one unique to Minnesota. The jury heard emotional “spark of life” testimony from Wright's father about how his son loved to play basketball and was a great dad to his own son. This was a page ripped from the Chauvin playbook, where Floyd's brother and partner offered the same kind of gut-wrenching evidence. Minnesota allows such testimony because, according to a court decision, it presents “the victim as a human being”. This is especially important in cases with Black victims, in which the defence strategy is often to depict the victim as a thug who got what he deserved.

But this kind of testimony is problematic because it should be irrelevant to the jury's determination of guilt or innocence. Whether the victim was a saint or sinner has no bearing on whether a crime was committed against him or her. That's why Minnesota is the only state that allows such evidence during trial. The danger is that some people's lives will be deemed more worthy of protection than others. And it's not hard to anticipate the racial impact of that calculus in a country that, as the Black Lives Matter movement likes to point out, remains tainted by white supremacy.

A racial-justice pragmatist might say that the Potter prosecutors did what they needed to do to secure a rare criminal conviction of a police officer for killing an unarmed Black person. Another racial-justice pragmatist might say that these kinds of prosecutorial power grabs will only come back to haunt people of colour because "bad apple" cops will not be their primary targets. Both would have a point.

Paul Butler writes on issues at the intersection of criminal justice and race. Butler is the Albert Brick Professor in Law at Georgetown University Law Centre and an MSNBC legal analyst.