Deep down, Detective Susan Logothetti knew she was knocking on the front door of a killer.

Undercover and on a risky mission, she stood on his doorstep that drizzly January day in Olympia, Washington, thinking how unlikely it was that her plan would nab him. Logothetti held her breath as she saw prime suspect Mitchell Gaff walking toward her. He opened the door.

Having read his lengthy case file, Logothetti knew the horrors that Gaff was capable of inflicting. He had committed some of the most violent rapes she had come across in her seven years as a detective with the Everett Police Department, just north of Seattle. Now for the first time, he was strongly suspected of committing a cold-case murder that was over four decades old.

Logothetti didn't flinch. She introduced herself to Gaff using a false name and a ruse that sounds straight out of a Hollywood crime series. Logothetti and two other detectives were at Gaff's house posing as chewing gum researchers who wanted him to sample their product.

In reality, Logothetti was desperate to collect Gaff's DNA to definitively link him to the cold-case killing. Dressed in lime-green T-shirts displaying a "Zolt Energy Gum" logo, Logothetti and the other female detective used their bubbliest voices and brightest smiles to deliver the pitch.

"We have this great new healthy energy gum and we're going to be launching it at Safeway, and we're looking for community members to sample it for us and help us pick which flavor we want to launch first," Logothetti told Gaff. "We tried to be as excited about it as we could."

It felt like a long shot.

"He is a diagnosed psychopath," Logothetti told USA TODAY in a recent interview. "Mitchell Gaff is a whole different animal."

Before Logothetti moved to the Pacific Northwest, the Illinois native was forging a career that would make her uniquely qualified to become a detective.

She worked with children who were victims of abuse at a foster care agency and then with felons as a probation officer. Each role gave her unique insight into both victims and offenders, and how to talk to them.

Logothetti joined the Everett Police Department in 2012 and became a sex crimes detective in 2019. She quickly became intrigued by the department’s only cold case detective and began asking him about his cases, and eventually, his upcoming retirement.

“I asked who was going to take over the cold cases when he retired and he said, 'Nobody, because nobody wants to do them,'” she recalled. “So I asked if I could do them.”

Logothetti got her dream job. She had been working cold cases for less than a year when she got the news that would end up changing her life and dozens of others.

The unit's previous detective had submitted a ligature used in the murder of 42-year-old Judy Weaver, a mother of two who was brutally raped and killed in her Everett apartment on June 1, 1984. The detective was convinced that Weaver's fiancé had killed her and he told Logothetti that the test should come back confirming as much.

But when Logothetti opened the report in late 2023, the name that matched the DNA was someone she had never heard of: Mitchell Gaff.

"I immediately looked him up. The first thing I saw was that Mitchell Gaff is a registered sex offender and deemed a sexually violent predator," she said. "Then I was able to get copies of Mitchell Gaff's prior crimes, and immediately I knew. He was the one."

When Logothetti read through Mitchell Gaff's case file, she knew she was reading about a monster.

A diagnosed sexual sadist, Gaff had been convicted of the violent sexually motivated attack of an Everett woman in 1979 and the prolonged 1984 rape of two sisters, ages 14 and 16, as their mother slept in the basement of their Everett home.

In the case of the sisters, Gaff hogtied the girls, cut off their clothes with a knife, raped them repeatedly, beat them, choked them, and shocked one of them with an electrical cord, court records say. The younger girl was able to escape and get help as Gaff began choking her sister with the electrical cord. They survived.

In the other case, Gaff attacked a woman as she was wrapping up some yard work in broad daylight the day before Thanksgiving in 1979. The woman, Jackie O'Brien, happened to be an officer with the Washington State Patrol who had interviewed rape victims and knew that she had to fight like a tiger.

After Gaff beat her head repeatedly with a gun and slammed it into a cement floor, he had her on her knees facing away from him when he began tying her up, she recently told USA TODAY. O'Brien saw a disturbing sex toy in his duffel bag and pounced.

"I threw my body against him and caught him off guard, and he kind of stumbled against the wall," recalled the now-76-year-old. "I stood up, and I was trapped, and he said, 'You're going to die now, you b----.' And I knew I was dead."

Gaff then pulled out a hunting knife and slashed O'Brien across a hand that she had held up in self-defense. "Then I shoved him and I went out one way into the garage and alley screaming," O'Brien said.

Gaff was arrested soon after but only got a slap on the wrist at trial. After a jury found him guilty of assault with a deadly weapon and burglary, the judge in the case sentenced him to 30 days of jail with work release and five years of probation.

Gaff was still on probation when he carried out the brutal attack on the teenage sisters.

Gaff was convicted of raping the sisters in 1984 and served about a decade in prison and in an intensive sex offender treatment program. When his sentence was up, unlike the vast majority of convicts, Gaff wasn't free to go.

Prosecutors wanted Gaff confined indefinitely under a new state law in Washington targeting violent rapists and child molesters who had finished their prison terms but were deemed likely to reoffend. After an ensuing court hearing, a jury found that Gaff was a violent sexual predator, allowing him to be kept under lock and key at the state's Special Commitment Center on McNeil Island in Puget Sound. The arrangement cost the state $550,000 a year, according to archived news reports.

In 2000, at the age of 42, Gaff again sought release. His therapists at the state's commitment center said they thought he was ready after years of intensive therapy, and he said he was a changed man.

"I have an incredible amount of remorse and pain for the innocent people I've harmed," he told the Associated Press at the time, saying that he had learned how to handle his emotions and empathize with his victims. "There was no excuse, no rationalization for what I did to people."

Another jury ruled in 2000 that Gaff was a violent sexual predator, and he remained on McNeil Island for another six years before he went on to win freedom.

Gaff has talked about why he attacked women in multiple interviews and court hearings, blaming months of sexual abuse by a female babysitter when he was a boy, combined with alcohol and drug abuse as an adult.

"I am not what I've done," he told GQ in 1995, saying a switch flipped after he underwent sex offender treatment. "A giant cog turned inside me, and I was like, 'Yeah! I got it!' It wasn't, 'Oh, I hope I never rape again.' It was, 'I know what to do now so that I don't rape anyone.'"

Police say there's no evidence that Gaff committed any crimes following his release.

Logothetti noted numerous similarities in Gaff's previous crimes to the cold case murder of Judy Weaver. They included hog-tying the victims, using the same type of ligatures, the location of the crimes and the gratuitousness of the violence in each case.

"All of these things kind of added up," Logothetti said.

Weaver was killed on June 1, 1984, at her apartment located halfway between where the attacks on O'Brien and the teenage sisters took place. It also came less than three months before the sisters' rapes.

Firefighters responded to a fire at Weaver's apartment and found her dead inside. Her clothes had been cut off, she was hogtied with an extension cord and a drawstring, and she had been raped, beaten, and strangled, court records say. A butcher knife was lying near her body, and the killer had started a fire.

Police suspected Weaver's fiancé but had no proof. Despite the striking similarities between her murder and the sisters' rapes, detectives didn't connect the dots at the time and the case went cold.

That is until 40 years later when Logothetti got the report that showed Gaff's DNA was on one of the ligatures in Weaver's case. But Logothetti needed to firm up the case and wanted more of Gaff's DNA.

For weeks, Logothetti conducted futile surveillance on Gaff, hoping he would discard something with his DNA on it, like a soda can or a wad of gum. When that didn't work, the idea of going undercover was born.

When Longothetti knocked on Gaff's door that drizzly day in Olympia, she didn't really expect him to talk to her. "When he answered the door in his pajama pants with his cat, it did take me aback for a second to see him right there in front of me like that," she said.

At first Gaff seemed a bit reluctant to fall for the gum ruse but Logothetti won him over with compliments and the promise of a Safeway gift card.

"I really was like, 'I don’t know, most guys in prison won't fall for something like this,'" she remembers thinking.

But Gaff is a diagnosed narcissist, which worked in favor of the detectives.

"He loves to talk about himself … He wants to be complimented," Logothetti said. "The other female detective was complimenting some of his artwork in the house and he was going on about that ... We were definitely complimenting his yard and house and art."

Gaff let his guard down and agreed to the survey, discarding multiple wads of chewing gum into carafes and handing them back to the undercover detectives.

"When he switched to a new flavor he's like, 'Oh I got to spit out this gum,'" Logothetti said. "When I saw him spit it into a carafe I really had to contain my excitement ... We were all giddy."

Just as detectives suspected, DNA from Gaff's gum came back in 2024 as consistent with vaginal swabs and a neck ligature taken from Weaver's body. He was arrested in May 2024 and was ordered held in jail until trial.

Logothetti thought that was it. Then in January 2025, she got a call from an angry man demanding to know why detectives had made no progress in their investigation of his wife's death in Everett in 1980. As the man described the murder, Logothetti immediately recognized "startling similarities" between the case and that of Weaver's killing.

On July 12, 1980, Susan Vesey's husband came home from work to find his wife brutally killed the day after her 21st birthday. Their 3-month-old baby was on the bed in the same room as his mother's body and their 2-year-old daughter was in a crib in another room.

Vesey had been hogtied, her clothes had been mostly removed, and she had been raped and strangled, court records show.

Logothetti submitted multiple items from Vesey's crime scene to the Washington State Patrol's forensic lab for updated analysis. In April 2025, DNA from a white cord used to bind Vesey matched Gaff, court records say. In March 2026, another piece of white cord from the crime scene matched Gaff, court records say.

Gaff was charged on March 13 with murder in Vesey's death. What he did next shocked police, prosecutors and his victims.

Gaff, now 68, had been set for trial in September on murder charges in the deaths of Weaver and Vesey. But he unexpectedly decided to plead guilty in April. He described the two murders in detail in open court as part of a plea agreement with prosecutors.

At his sentencing in May, family members who had waited more than four decades to find out who killed Weaver and Vesey were at last able to confront him in court.

"I was in the same room when the defendant killed my mother ... I was found swaddled on her bed. This is the beginning of my life," Vesey's son, Joshua Vesey, said in a statement read during the sentencing hearing. "What the defendant took from me and my sister was not just a life − it was a mother's unconditional love, the kind of love that shapes who you become before you can understand it."

Before Gaff was sentenced, prosecutor Craig Matheson emphasized to the judge "the predatory randomness" of Gaff's crimes.

"He is in fact the bump in the night that should make people aware that there is mortal danger at hand," Matheson said. "It could have been anyone that caught his attention"

Gaff also addressed the court, showing little emotion while saying that he was “without excuse or defense” and apologizing to his victims and their loved ones. "Nothing I can say or do can make up for what I’ve done," he said.

The judge sentenced him to 50 years to life in prison, all but guaranteeing that Gaff will die behind bars.

It was one of the most gratifying days in Logothetti's career. She sat front and center during the hearing and enjoyed watching Gaff get angry when Jackie O'Brien confronted him about his attack on her.

With all the horrors and terror that Gaff inflicted on women, his courtroom exit felt appropriate.

"After sentencing I handcuffed him and walked him back to the jail with the correction officers," Logothetti said. "It was kind of for my own closure. But I also think a female really needed to be the one to cuff him."

This article originally appeared on USA TODAY: Detective details undercover ruse that nabbed serial killer Mitch Gaff