Late one night in the spring of 2012, Anthony Finnelly and his fiancée got into an argument at their home outside Dallas — he’d been drinking, so she wanted his gun for safekeeping, records show.

Finnelly wouldn’t tell her where the gun was. She stepped outside with their dogs and soon felt such a sharp pain in her legs that she thought she might have been bitten by a snake, according to one of several statements she gave to McKinney, Texas, police.

Actually, Finnelly had shot her, with the bullet piercing one leg and lodging in the other. According to varying accounts the police got, she was either shot from inside, through a window, or the couple struggled for the handgun as it went off.

The woman later told a detective that “emotionally she wants to believe the shooting was an accident” — as Finnelly maintained, telling the cops he was inside, tripped with the gun in his hand and that it went off — “but intellectually she realizes that is unlikely,” the records show.

He was charged with aggravated assault, a felony.

While the case was pending, he moved back to his native Chicago, where, in July 2013, he started a new job — as an investigative aide in the Cook County medical examiner’s office.

The following month, Finnelly pleaded guilty to a reduced charge of misdemeanor assault. He was sentenced to a year in jail and fined $500 — though his jail term was suspended, and instead he ended up on probation for just under a year, records show.

Finnelly’s assault conviction didn’t prevent him from staying on with the medical examiner’s office, where he has since been promoted to investigator and now makes $53,000 a year.

The medical examiner’s office has been the subject of a series of investigative reports in the Chicago Sun-Times in recent months — over hiring and promotions practices and also over the conduct of the office.

Last month, the Sun-Times reported that the medical examiner’s office is conducting an unprecedented review of more than 200 cases handled by a former county pathologist, Dr. John Cavanaugh.

That was after the agency — which is run by Dr. Ponni Arunkumar, the chief medical examiner, under the authority of Cook County Board President Toni Preckwinkle — found that Cavanaugh had made errors including missing a murder.

Cavanaugh had found “no clear evidence of trauma” on a man whose decomposing body was found in a burning building but with no sign of burns. Cavanaugh labeled the cause of death as “undetermined.”

Another pathologist later reported finding that the man had suffered multiple wounds from an assault and changed the ruling on the cause of death to homicide.

In January, the Sun-Times reported that the FBI believes Arunkumar’s office botched another case, erroneously finding that Chicago police Sgt. Donald Markham shot himself in the head in 2015. Federal agents believe he was murdered, based on an investigation that included a review by a pathologist who formerly worked for the Cook County agency. Arunkumar stood by the suicide ruling.

Finnelly, 59, won’t comment on his conviction except to say, “My employer is aware of it.”

Asked about Finnelly, Cook County spokeswoman Becky Schlikerman says, “We do not discuss personnel matters as it relates to individual employees.”

But Schlikerman says “a review by the Bureau of Human Resources has found all hiring policies and procedures are in compliance in this case.”

People applying for a county job aren’t required to disclose past arrests, according to Schlikerman — only criminal convictions.

She says that anyone already working for the county who is arrested or convicted — over any on-duty or off-duty incident — is required to notify a supervisor but that this doesn’t “automatically” mean the employee will be fired or otherwise disciplined.

Finnelly isn’t the only medical examiner’s office investigator hired despite legal troubles or disciplinary problems.

In February, the Sun-Times reported that Jerold J. Rodish landed a job with the medical examiner’s office in 2012, several years after the Cicero Police Department fired him as a commander for failing to disclose an arrest record on his employment application. Rodish also was the subject of lawsuits, accusing him of sexual harassment and excessive force, that Cicero settled for a total of more than $1 million.

Lawrence Santoro Jr., a medical examiner’s investigator since 2012, was a detention officer for the Berwyn police until he resigned after being accused of leaving a detainee unattended. When a police officer confronted Santoro about where he had been, reports say he answered, “I was f—— relaxing.”

The medical examiner’s office has disciplined Santoro for infractions including threatening to throw his supervisor “out of a window” during an argument over whether to visit the scene of a death.

Medical examiner’s investigators are required by law to visit the scene of all violent and suspicious deaths, but the Sun-Times has reported that, over the past several years, they in fact have gone out on fewer than one of every five cases. County officials have said the investigators can provide important perspective to the pathologists trying to determine the manner and cause of death.

Since September 2014, Finnelly has visited the scene in 294 of 850 cases, according to county records — just over one-third.

Finnelly also previously has worked as a police officer in Westchester. Not long before the 2012 shooting, he was “terminated” as an investigator for an insurance company in Texas, which he disclosed on his county application.

After shooting and wounding his fiancée, Finnelly brought her inside the home and called 911, according to police records that indicate he wouldn’t answer questions from the dispatcher.

Finnelly then drove off, records show.

“He left me,” his fiancée told one officer. “He was more interested in saving himself instead of helping me.”

After driving away, Finnelly called his brother, who is a police officer in the south suburbs. The brother told an investigator that Finnelly had told him he’d “f—– up,” and “it wasn’t for her,” according to records that say the brother encouraged Finnelly to go back to the scene of the shooting, and he did.