When Judge Peter Cahill takes the bench in Minneapolis Friday for the sentencing of Derek Chauvin, he will set about doing something that is an extreme rarity in the U.S. legal system -- punishing a now-former police officer convicted of murder while on duty.

In the past 16 years, just nine law enforcement officers have been sentenced to prison terms after being convicted of murdering people on the job, according to data released this week by the Police Integrity Research Group at Bowling Green State University, which tracks police arrests and prosecutions.

Chauvin, 45, who was convicted by a Hennepin County, Minnesota, jury of murdering George Floyd in 2020, is expected to be the tenth, according to the data the group has been collecting since January 2005.

The eleventh may come in quick succession, though, when William Darby, a Huntsville, Alabama, police officer convicted of murdering a suicidal man, Jeffrey Parker, in 2018, is sentenced in August. An officer took the witness stand against Darby and testified she was attempting to de-escalate the situation after Parker threatened to shoot himself when Darby, who is still on the force, killed him.