The Chicago Police officer had put her gun on the kitchen counter for only a second. But that was just long enough for a fellow cop, probationary Officer Ruby Falcon, to snatch it and hold it to her head.

Hours earlier, there had been few signs that the night of drinking and dancing in July 2016 would end in bloodshed in a Southwest Side house filled with at least six cops.

But that’s exactly what happened around 4 a.m. that summer morning: Falcon, authorities say, took her own life using her fellow officer’s weapon.

The whole tragic tale — not publicly known until now — is the subject of a recently filed wrongful-death lawsuit. It also touches on some of the key issues facing a Chicago Police Department that’s struggled with how to deal with mental illness among its ranks and a police disciplinary system that has been under fire.

Looking back, another officer would acknowledge “the formula” had come together in Falcon’s life: Someone she knew in high school had been charged a few months earlier with attempted murder for attacking Falcon; a bank was coming for her home; and Falcon, who worked for the Cook County Sheriff’s office between October 2007 and February 2015 before joining CPD, had apparently been taking anti-depressants and had made suicidal comments, according to an Independent Police Review Authority report.

Then, Officer Danielle Deering left her gun on her kitchen counter in the early morning hours of July 30, 2016. Deering assumed the weapon was safe, as several police officers had gathered at her house to celebrate Deering’s upcoming transfer to the CPD bicycle unit.

Deering and Falcon had been together throughout the night. When they got back to Deering’s house, an intoxicated Falcon became upset that Deering had left her alone with the other officers.

Investigators were told the following happened next:

Falcon, 31, believed a former romantic partner — also a probationary officer — was hiding in Deering’s home. She began to yell, telling Deering not to “f—ing lie.” Deering tried to calm her down. She turned to close the door to her basement, where other officers were socializing.

When she turned around, Falcon had Deering’s gun to her head.

Deering pleaded with Falcon. She tried to hand Falcon her cellphone, saying, “here’s your phone, call her, call her.” It wasn’t enough.

“I’m not crazy,” Falcon yelled. “I’m not f—ing crazy. I’m not crazy.”

Then Falcon pulled the trigger.

Deering cried for help. The other officers rushed up from the basement. Another had just arrived at the back door and found Falcon face down on a bloody kitchen floor. He helped a shaken Deering walk outside and called 911.

A deputy chief who helped investigate the shooting later found Deering in her basement. He said she repeatedly told him, “It’s my fault. It’s my fault.”

The lawsuit filed in Cook County Circuit Court by Falcon’s family names as defendants Deering, the city of Chicago, and two bars where Falcon and Deering had been drinking. The family is alleging Deering’s failure to protect her weapon, as well as the bars serving alcohol to Deering, led to Falcon’s death.

Unlike other cops who have been given penalties up to termination for incidents in which they left their guns unattended, IPRA didn’t recommend discipline against Deering for failing to secure her off-duty weapon. The police investigative body did, however, recommend a 10-day suspension for Deering for taking her gun to the two bars in the hours leading up to Falcon’s death.

Falcon’s death added to a suicide rate at CPD that is 60 percent higher than other departments across the nation, according to the U.S. Justice Department.

But the Falcon family’s attorney, Antonio Romanucci, also said he is troubled by a pattern of injuries and deaths involving Chicago police officers’ weapons, which suggests officers are not following orders to secure their guns. When asked about IPRA’s decision not to fault Deering for leaving her weapon unsecured, Romanucci said, “the city of Chicago continues to carve out exceptions to the rules that don’t exist.”

IPRA concluded “there is no evidence to suggest foul play” by anyone in Deering’s home the night of Falcon’s death, including Deering. No gunshot residue was found on Deering’s hands nor was it found on Falcon’s, according to IPRA. However, the Falcon family’s lawsuit accuses Deering of changing her story after the shooting.

Attempts to reach Deering for comment were unsuccessful.

Chicago Police followed IPRA’s recommendation and suspended Deering — who briefly served in the bike unit and is now assigned to the Gresham District on the South Side — for 10 days, according to department spokesman Frank Giancamilli. However, she appealed the suspension and has not served it, pending the appeal’s outcome with an independent arbitrator.

Giancamilli added that during her brief time with the CPD, Falcon — who was also assigned to the Gresham District — was never the subject of any disciplinary action. Citing privacy laws, he wouldn’t disclose whether Falcon exhibited any signs of mental instability before she was hired.

During her tenure with the sheriff’s office, Falcon was not disciplined for any misconduct, and there was no “indication for concern for her mental health,” said Cara Smith, chief policy officer for Cook County Sheriff Tom Dart’s office.

When IPRA cleared Deering of wrongdoing for not securing her firearm, it pointed to an Illinois statute designed to protect young children in homes with guns. IPRA noted, “the only existing directives from Chicago Police Department regarding the storage of firearms rely upon adherence to this specific statute.” Deering’s only guests were Chicago cops, so IPRA said the rule didn’t apply.

Deering told IPRA investigators she set down her gun because her holster had broken during the night, and wearing it had become uncomfortable. She also said she didn’t plan to “really drink” at the two bars she visited in the hours leading up to Falcon’s death: 115 Bourbon Street in Merrionette Park and Bar 122 in Alsip. Bar 122 declined to comment, and 115 Bourbon Street did not return calls.

Deering said she had begun to carry her weapon more often while off-duty after running into people she had arrested who then made comments about her job. She also cited the “recent events that took place in Florida.” An investigator took that to be a reference to the Pulse nightclub shooting in Orlando.

Falcon and Deering became close in the final months of Falcon’s life, opening up to each other about their relationships and break-ups, records show.

A former high school friend of Falcon’s, Christian Garduno of Lansing, appers to have been obsessed with Falcon, according to IPRA and court records. Garduno allegedly attacked Falcon three months before her death, punching her and bashing her head with a bottle. Garduno faces several criminal charges stemming from the attack, including attempted murder, records show. Meanwhile, the officer told IPRA that Falcon “wasn’t right” after the attack.

An officer who wasn’t in Deering’s home at the time of Falcon’s suicide, told IPRA about a suicidal comment by Falcon. She said Falcon pointed a gun at her in 2010 and said “I should just f—in’ kill you.” Later, she said Falcon went to her bedroom, pulled a gun out of a dresser drawer, pointed it at her own head and said, “I just want to f—ing die.”

However, none of the officers in Deering’s home the morning of Falcon’s death acknowledged knowing about such comments by Falcon, according to Cook County Medical Examiner’s office investigators.

Deering told IPRA she planned to go out early on July 30, 2016, with another unnamed probationary officer with whom Falcon had a previous romantic relationship. Falcon joined them at 115 Bourbon Street around 12:30 a.m., Deering told IPRA. While they were there, the other officer’s girlfriend showed up, and Deering said Falcon seemed “thrown off” or “upset.”

Deering, Falcon and the third officer left 115 Bourbon Street around 2 a.m., riding with the third officer to Bar 122. All three appeared to be drinking in surveillance video from both bars inspected by IPRA, records show.

After an hour, Deering and Falcon hopped in an Uber — and that’s when Deering said she bent her holster. The car took them back to their cars at 115 Bourbon Street. But because Falcon was too drunk to drive, Deering told investigators she drove them both back to her house, leaving Falcon’s car behind.

During the drive, Falcon spoke on her cellphone’s speakerphone to the third officer, who invited Falcon to her house before eventually changing her mind and rescinding the offer. Deering said she told Falcon her relationship with the third officer was unhealthy. She said Falcon agreed and gave Deering her cellphone.

When they arrived at Deering’s house in the Clearing neighborhood, they were joined by four other officers and all gathered in the basement, Deering told investigators. Then Deering said she then went upstairs to grab beers and make a bed for Falcon.

Deering said she walked into the kitchen, took some beers from the refrigerator and set them on the counter. Then she placed her holstered weapon on the counter.

She said she ran into Falcon while heading back to the basement to get linens. The other officers said Falcon had been in the basement bathroom and was clearly drunk.

After Falcon shot herself, authorities found Deering’s gun under her body. A toxicology report confirmed her blood-alcohol level was more than twice the legal limit to drive.

While Deering told IPRA she put her gun on the counter, a police report provided by Romanucci only mentions that Falcon grabbed Deering’s “holstered weapon.” Further, the Falcon family’s lawsuit alleges that Deering told investigators she “was wearing her service weapon in a holster on her side when Ruby Falcon grabbed the weapon.”

The lawsuit alleges that Deering later told investigators she placed the weapon on the kitchen table near Falcon and left the room to make her bed, claiming Falcon shot herself while Deering was in a bedroom.

Such conflicting statements appear in other cases.

Romanucci also represents the family of Michael LaPorta, who visited the home of Chicago Police Officer Patrick Kelly in January 2010. There, Kelly’s service weapon allegedly discharged and fired a bullet into the back of LaPorta’s head, leaving him disabled and leading to the family filing a lawsuit. Kelly remains a Chicago police officer but is on administrative duty.

In another case, the Chicago Police Board fired Steven Lesner in 2014 over the February 2009 death of Catherine Weiland. Lesner was an Albany Park District sergeant when he answered Weiland’s call for help during an argument with her boyfriend. Lesner drove her home — buying her a bottle of wine along the way — and later returned to her apartment with more booze after his shift ended.

Lesner said he placed his loaded auxiliary weapon on the floor next to a love seat where he had been sitting in Weiland’s apartment while they watched TV together. He later got up to go to the bathroom. That’s when he said he heard a gunshot and found Weiland in a chair with his gun in her lap.

Lesner originally was given a suspension over the incident, but the police board moved to fire him after a series of Chicago Sun-Times stories about Weiland’s death. The police board said leaving the weapon unsecured was one of a “series of calculated and knowing decisions” made by the officer.