Phoenix police officer Mark Rine was a few minutes from his shift ending in the early hours of November 6 when he was told that he and other officers were expected to work late, KPNX reported.

“I’ll be going upstairs to fill out my resignation letter then,” Rine, a 14-year veteran of the department, responded.

He went on to summit that resignation later that day, saying he was quitting because he was overworked and underappreciated.

“I will no longer work in an environment where I do our squad and shift’s work, do my own, and then be demanded to do the next shift’s work as well,” he wrote in the letter, according to the station.

“I will no longer work in an environment where a Lieutenant punishes an entire squad, and holds over an entire squad because one or two people will not ‘volunteer’ to hold over.”

He added: “I am tired of being used, being abused, running on little food, and little sleep. I resign my position. God will provide.”

A spokesperson for the Phoenix Police Department told Newsweek that it was “aware of an internal memorandum circulating publicly,” but that Rine remains employed by the police department. “It would be inappropriate for us to respond to this private personnel matter at this time,” the spokesperson said.

The spokesperson added that on the night of November 5, the Cactus Park Precinct had been working two critical incidents: a triple shooting with one fatality and a fatal hit-and-run collision with downed powerlines.

“Both incidents were still early in the investigative stage as second shift officers were nearing the end of their shift. Both scenes tied up more than a dozen officers from both second and third shifts,” the spokesperson said. “The Phoenix Police Department’s number one priority is to answer emergency calls from our community members. In order to ensure enough officers were free to respond to calls for help, the on-duty lieutenant held over three second shift squads for two hours past their scheduled release time in order to provide proper coverage for the area.”

Rine could not immediately be contacted for comment.

Rine’s letter has drawn further attention to the police department’s staffing shortage and struggle to recruit new officers. At a meeting on Wednesday, the police department’s Executive Assistant Chief Michael Kurtenbach said the department was losing officers “at an accelerated rate.”

Kurtenbach said the department was 51 patrol officers shy of the 1,096 considered “minimum staffing,” according to KPNX.

More than 200 officers have left the department in 2021, he added, and about 40 more are expected to leave by the end of the year.

“Just as calls for service are going up, violent crime is going up. Response times are going up,” he said. “At some point, we’re going to have to seriously look at redeploying resources that already exist if we can’t bring new officers through the door.”

It comes after the Department of Justice launched an investigation over the summer to examine if Phoenix police officers are using excessive force or abusing people experiencing homelessness.

The probe will also examine whether police have engaged in discriminatory policing practices and will work to determine if officers have retaliated against people engaged in protected First Amendment activities.

Rine, who is white, previously made headlines after fatally shooting Rumain Brisbon, an unarmed Black man, in December 2014.

The shooting came in the same week a grand jury decided not to bring criminal charges against a white police officer over the death of Eric Garner, sparking protests around the country.

No criminal charges were filed against Rine, but the city of Phoenix agreed to a $1.5 million settlement with Brisbon’s family.

Update 11/15/21, 10:45 a.m. ET: This article has been updated with comments from the Phoenix Police Department.