The sheriff's captain said she didn't want the murder suspect to know law enforcement was on to him when they pulled him over for thumbprints and a photo.

So the Florida official told a deputy to pretend he was making a traffic stop based on race, audio shows.

“We want it to look like you're the grumpy old man,” a woman the Monroe County sheriff's office confirmed to be captain Penny Phelps says in a recording now made public. “You have nothing better to do than, you're the white supremacist, you're messing with the black guy who's riding his bike.”

The sheriff's office quickly took Ms Phelps off the murder case last month and opened an internal investigation after receiving allegations of misconduct, spokesman Adam Linhardt said. Last week, they also removed Ms Phelps as commander of the major crimes and narcotics units, according to documents shared by the agency.

Deception is widely accepted as a valuable and often legal tool for criminal investigators. Police officers routinely go undercover to get incriminating statements, and judges have upheld confessions induced in part by false information. The Supreme Court has stated that “stealth and strategy” are “necessary weapons” for officers.

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But critics are leery of Ms Phelps's willingness to play into documented racism and racial profiling among some members of law enforcement - issues ranging from “driving while black” to offensive social media posts that have sown mistrust.

Ronnie Dunn, a professor at Cleveland State University who studies policing, said he understands why some may see Ms Phelps's advice as another example of police misleading a suspect to solve a heinous crime. A green light for an officer to project discrimination, though, strikes him as unethical.

“We already know that that's a charge that has a lot of validity to it, in a lot of areas in this country,” said Mr Dunn, who also serves as Cleveland State's chief diversity and inclusion officer.

Ms Phelps, who did not respond to enquiries Monday, told the Miami Herald that she cannot discuss a case under investigation but will be “happy to talk” once it ends.

Likewise, Mr Linhardt said the sheriff's office is legally unable to speak to many details of an ongoing case. He declined to say whether Ms Phelps's instructions were followed, what penalties she could face or what other complaints were lodged against the captain who has spent nearly two decades with the agency.

Officials say they have yet to determine whether Ms Phelps violated policy and have made no change to her annual salary of about $110,000 (£84,000). They have not said why the sheriff's office moved just recently to strip her of her command position.

They emphasised, though, that they are taking concerns seriously.

“Without regard to any specific case, rest assured that I will not tolerate discrimination or any misconduct by sheriff's office members, particularly misconduct that diminishes the trust our community has in this office,” Sheriff Rick Ramsay said in a statement. “When such matters are brought to my attention, I will address them in the appropriate and transparent way that you have come to expect from me.”

He told the Miami Herald that “not everything we do is going to be perfect.”

“When we do something wrong, we do whatever we can to hold ourselves accountable” he said.

The recording of Ms Phelps surfaced when prosecutors in a 2017 murder case turned materials over to defence attorneys, Mr Linhardt said. Ms Phelps instructed a deputy to accost Rory Wilson, one of two men accused of carrying out a fatal stabbing in a trailer park treehouse - a crime authorities have dubbed the “treehouse murder.” A third man is charged with driving the getaway car after a drug robbery turned violent, leaving another victim with a cut throat.

The Washington Post could not reach Mr Wilson, 52, and his attorney did not respond to a request for comment.

In the recording, Ms Phelps seems to be talking over the phone to deputy Lee Malone, who also did not immediately respond to requests from The Post. The audio was captured in the area of an interview room at the sheriff's headquarters, where equipment records continuously, Mr Linhardt said.

Only Ms Phelps's end of the conversation can be heard as she tells Mr Malone to wait for Mr Wilson and then make a traffic stop.

“I just want you to be the neo-Nazi who's picking on the black guy riding the bike,” Ms Phelps says.

She reiterates the goal later on to others.

“He knows his bit,” she tells them. “It's the white supremacist cop picking on the poor black guy that's riding on a bike.”

The recording eventually made its way to attorney Cara Higgins, who represents the man accused of driving the getaway car. She says her client, John Travis Johnson - who says he's innocent - included the white supremacist comments among many concerns about defendants' treatment in a fall letter to law enforcement that Higgins believes was “eye opening” for the sheriff's office.

The recording has fuelled Ms Higgins's concerns about the treehouse murder investigation, as local media report the Monroe County state attorneys office removed a lead prosecutor under the Florida Bar's scrutiny for allegedly withholding evidence. It's also bolstered her previous efforts to get Ms Phelps taken off the treehouse case, she said.

Now, Ms Higgins wants Ms Phelps dismissed from the agency.

“Anyone who uses those words has no place in that department at that level,” she said.

Mr Dunn, the university professor, said it's not clear from the details available whether Mr Malone could have violated the suspect's civil rights in following his superior's directions - something Mr Linhardt said the sheriff's office cannot speak to at the moment. In fact, Mr Dunn said, the actions were “probably legal.”

What Mr Dunn could say for sure: “I have never heard of anything quite like this.”