A federal jury needed little time last week to convict two Los Angeles County sheriff’s deputies for beating an inmate with mental illness and filing false reports to cover up the assault. Convictions stemming from the scandalous abuse in the jails have become commonplace – 21 current or former L.A. County Sheriff’s Department members have now been convicted.

This case stemmed from a 2010 incident in which deputies kicked, punched and pepper sprayed the inmate in a locked hallway, out of sight of surveillance cameras, as punishment for having been disrespectful. The deputies then cooked up a story to justify the beating, claiming the inmate left his cell without permission, ignored orders to return to it and instead walked into the hallway, where he tried to punch a deputy and violently resisted being restrained. The deputies even went so far as to leave certain deputies out of their reports because they had been involved in too many other force incidents.

Now, police lying shouldn’t be news to anyone. A poll last year found that one in three Americans believe police routinely lie. Residents of Los Angeles don’t have to look too far for evidence of police dishonesty. Disgraced former L.A. County Sheriff Lee Baca pled guilty to lying to federal agents investigating civil rights abuses in the jails, and a federal jury convicted Baca’s second-in-command – former Undersheriff Paul Tanaka – of obstruction of justice for interfering with that investigation.

In jail settings we should be particularly wary about the potential for police dishonesty. The ACLU of Southern California (ACLU SoCal) published reports over several years compiling inmate complaints of brutal violence at the hands of L.A. County sheriff’s deputies. Baca reflexively responded to these complaints with the refrain that inmates lie and exaggerate—and it unsurprisingly worked.

We as society are told, over and over, that those imprisoned are the worst of the worst and cannot be trusted. As a result, many in the public don’t care what happens to inmates or feel they deserve whatever they get. And for others the jails are simply an instance of out of sight, out of mind. Despite our long-term societal addiction to incarceration, relatively few of us will ever see the inside of a jail, and fewer still will think very long about what happens there.

For these reasons we should be on the lookout for police officials and agencies that whitewash inmate allegations of abuse. A key tell-tale sign is the investigation that relies exclusively on statements made by the officers involved and fails to include available civilian witnesses. In many instances documented by ACLU SoCal, chaplains and volunteers who witnessed inmate abuse made themselves available to investigators, but were never questioned.

The deputies who beat inmates and lied about it acted with impunity because they knew just how cursory the investigation into the beating would be and that no one in the department would ever believe the victim. It’s why officers lie – because they know they can get away with it.

Police know that in a typical swearing match, where it is their word against someone else’s, they will likely win. Notwithstanding the percentage of the people who believe police lie regularly, police still receive high honesty ratings, with 56% of Americans giving them a very high or high score. A deputy’s odds of winning a swearing match only improve when he squares off against, say, an inmate in the jails – the deputy knows full well how little weight the inmate’s testimony will carry. What little doubt remains can be practically eliminated when multiple deputies give corroborating testimony.

It’s why officers lie – because they know they can get away with it.

Who are prosecutors, judges and jurors going to believe? That’s the tempting question that leads down the rabbit hole where officers end up brazenly and coolly beating an inmate and lying about his being the aggressor.

Before anyone concludes that this is just a case of a few bad apples, remember that these were training officers who were trying both to teach an inmate a lesson and educate a young recruit in how things get done in the jails. They were trying to perpetuate a culture that the leadership either encouraged or condoned.

Human nature and history should have taught us by now that if power can be abused, it will be abused. We must put specific checks and balances in place to test the veracity of police – not because they are less trustworthy than others, but because they have been deemed credible and therefore given the power to lie.

Hector Villagra is executive director of the ACLU of Southern California. Follow @OHectorV.