A bumper pay hike for Phoenix police has been condemned by community advocates who argue the money should be spent tackling the city’s extreme heat, homelessness and mental health crises.

At a heated city council meeting on Wednesday, several public speakers questioned the $19.8m salary windfall given the continuing Department of Justice investigation into the city police department over allegations of excessive use of force, retaliation against Black Lives Matter protesters, discriminatory policing and inappropriate treatment of homeless and disabled people.

The federal investigation was launched by attorney general Merrick Garland in August 2021 amid mounting evidence of disproportionate use of violence against people of color and rising rates of police shootings.

“There is such a crisis of poverty and unhoused people in the city, yet every year more money goes to a police department which is fundamentally corrupt, under investigation and which has shown no changes in the culture from when they arrested protesters on false charges,” said resident Christopher Martinez.

But city officials argued that the salary bumps, which range from 20 to 67%, will help recruit and retain officers to the beleaguered department and improve policing. It was approved by the Democratic led city council by eight votes to one.

“You’re not twiddling your thumbs, you’re doing really important work out there and it is fair that our compensation reflects what we are doing,” said Mayor Kate Gallego.

Councilman Carlos Garcia, the lone vote against the pay hikes, said: “We’re embarrassed weekly on the nightly news, we pay out millions in lawsuits [against the police]. “We continue to prioritize and fund this department and then expect them to do things that they’re simply not trained for, and the results have unfortunately been loss of life.”

In one recent incident, Caleb Blair, a 19-year-old Black homeless man who was showing signs associated with heat stroke and possible intoxication, died in police custody last Friday during the season’s first extreme heat wave. According to local reports, Blair was rolling around the ground partially dressed after being asked to leave a convenience store where he had sought relief from the scorching 112F (44C) heat.

According to his family, who spoke to Phoenix New Times, Blair was addicted to fentanyl, the synthetic opioid that is 50 to 100 times more potent than morphine. Substance use played a role in 60% of last year’s record heat death toll.

The police have said Blair was “showing signs of impairment” but did not respond to the Guardian’s questions about why he was handcuffed. An internal critical incident inquiry is expected to provide video and audio footage of the fatal incident on 10 June. The medical examiner’s investigation is continuing.

Of the country’s 10 largest forces, Phoenix police department ranks number one for use of deadly force, according to analysis by Mapping Police Violence. Police shootings hit record levels in 2018 in Phoenix, the country’s fifth biggest city, topping New York, Los Angeles, Chicago and Houston.

The department, which has a budget of $850m, has hundreds of vacancies.