In May 2014, Patrick Baker and two accomplices set out to rob a house in Knox county, Kentucky. Baker knew the hardest part of the home invasion would be getting past the front door, so he devised a plan to dress up as police officers conducting a routine investigation.

Once inside the Mills family home, Baker revealed his true colours. He tied up the mother of the family, ignoring the pleas of the three children present, stole money and objects, then turned a gun on the father, Donald Mills, shooting him dead.

When Judge David Williams sentenced Baker in December 2017 to 19 years in prison for reckless homicide, burglary and impersonating a police officer, he said he would have given a longer punishment if he could. “I’ve been practicing law for 30-something years, and I’ve never seen a more compelling or complete case, the evidence was just overwhelming.”

Fast-forward just two years and Patrick Baker is a free man, released by Kentucky’s outgoing governor in act that has been dubbed “extreme pardon”. The brutal killing is just one of the extraordinary elements of the eleventh-hour move by Matt Bevin, a Republican in the Donald Trump mould who even by his own controversial record has astonished and angered his state with his pardons.

It was the final manoeuvre of a governor who was elected in 2016 on Trump’s coat-tails, making Kentucky the last southern state in America to turn Republican, only to be voted out of office last month. What motivated a politician who has spent the past three years waging bitter wars with teachers, trade unionists, voters, liberals, scientists and reproductive rights advocates suddenly display such profuse mercy towards prisoners has become the talk of Kentucky.

Even his own previously loyal Republican peers have expressed bewilderment. The top Republican in the state senate has called for an investigation of Bevin’s “extreme pardons and commutations”.

Mitch McConnell, the US senator from Kentucky better known as the Republican trying to stymie Trump’s impeachment trial in Congress, has denounced the release of “heinous criminals” in his home state as “inappropriate”.

Speculation of what drove Bevin to his action initially focused on money, after the Louisville-based Courier Journal discovered that the family of Patrick Baker had donated $21,500 to Bevin’s political campaign funds before the commutation. Suspicion of pecuniary incentives then turned to moral outrage of a different sort after Bevin tried to explain on local radio why he had pardoned Micah Shoettle after only 18 months of his 23-year sentence for rape.

“There was zero evidence,” Bevin told the radio host, adding that the girl’s hymen had been intact.

That provoked a whole new chorus of indignation, including from paediatricians who pointed out that rape cannot be proved or disproved by examination of the hymen.

That was just the start of it. As intrepid local journalists began to dig into the mountain of pardoned cases, other apparent horrors emerged.

They included further sexual offenders. Dayton Jones, who Bevin set free after three years of a 15-year sentence, had pleaded guilty to raping a boy aged 15 whose bowel he ruptured with a sex toy. Charles Phelps had his name removed from the sex offender registry by Bevin having pleaded guilty in 2013 to child abuse images offences and sexual conduct with minors.

The gruesome details of the violent crimes committed by some of those selected for commutation did not stop there. Delmar Partin was convicted of beheading a female co-worker and hiding her mutilated body in a barrel; Irvin Edge had hired a hitman to murder his business partner at home in front of his family; Blake Walker had killed his own parents.

Most of the lucky 428 singled out by Bevin were non-violent. When the Courier Journal came to analyse the beneficiaries of his largesse, the paper found that 336 of them were on non-violent drug sentences.

But therein lay another discrepancy. Within that group, 95% were white. That’s in a state in which 20% of inmates on drug convictions are African American or from some other minority community.

The newspaper calculated there were almost 1,000 black or other minority prisoners who would have qualified for Bevin’s largesse. He chose 16.

On one level, there is something fitting about the storm of controversy in which Bevin has finished his governorship given that disputes seemed to follow him around throughout his term in office. At the height of a recent measles epidemic, he let it be known that he had exposed each of his nine children to a neighbor’s chickenpox so that they would contract the disease as an alternative to getting vaccinated.

“They were miserable for a few days, and they all turned out fine,” he said, while telling the federal government to get its nose out of people’s private business. That anti-vaxxer sentiment expressed by Kentucky’s then governor earned him a riposte from a leading paediatrician who remarked: “We’re no longer living in the 17th century”.

Earlier this year, when Kentucky schools were closed to protect children from the -20F (-29C) wind chills, Bevin publicly complained: “C’mon now. I mean, what happened to America? We’re getting soft.”

On policy, he followed the classic Trump textbook, ramming through “right-to-work” laws that prevent trade unions gathering fees as a condition of employment, denouncing teachers on strike for exposing kids in their charge to sexual abuse and physical danger, supporting efforts to suppress the vote among minority communities, limiting access to Medicaid and banning abortion at 20 weeks.

The toxic combination earned him Trump’s adoration – the US president unsuccessfully campaigned on Bevin’s behalf in the recent gubernatorial race – but it also gained him the mantle of one of the most unpopular governors in the US.

Last week Bevin posted a long screed on Twitter in which he sought to explain his pardons. He began by evoking the spirit of redemption and second chances, and the ambition to help offenders seek rehabilitation.

He went on to insist that during his years as governor he had invested hundreds of hours to reviewing petitions for pardon. “Contrary to that which has been falsely stated by many, not a single person was released who had not already been scheduled for a specific release date,” he said.

He denied any financial motive, calling any such suggestion “highly offensive and entirely false”.

The Twitter thread does not appear to have satisfied his detractors, or calmed the widespread shock at a Republican’s last-minute flurry of pardons. The sister of the murdered home owner, Donald Mills, was blunt after she learnt that Patrick Baker was now out.

“Matt Bevin can rot in hell,” she said.