BOISE, Idaho — Frank Abbott Sweeney thought he had done everything right.
For years, the 76-year-old had been wiping his fingerprints off the malice-laced postcards he sent out by the dozens to terrify and smear members of a Boise family.
He had cleaned each of them of any trace of DNA. He had mailed the cards from different drop-off boxes each time. He had paid the postage in cash.
So when federal investigators were waiting with a warrant when he pulled into his driveway in early March of 2019, he had only one question.
How did you catch me?
"Mr. Sweeney was pretty good at covering his tracks," investigator Darin Solmon with the U.S. Postal Inspection Service said. "Well, he slipped up. And everybody slips up. It's just a matter of time."
Investigators agreed to sit down with KTVB to detail the case and how they ultimately caught up with the culprit behind one of the most extreme stalking cases their office had ever handled.
The Garden City man's arrest and ultimate incarceration put an end to a nightmarish ordeal of anonymous threats, lies, and surveillance that boiled over from a parking lot argument in December of 2015.
The victim, a Boise resident, had scolded Sweeney for parking in a handicapped spot without a handicap placard on his pickup at the Garden City post office on Marigold Street.
The confrontation between the two strangers was brief, but Sweeney couldn't let it go, Solmon said.
"His motivation was basically revenge and embarrassment of people he felt had embarrassed him," he said. "I think he felt entitled to do what he did. I think deep down in his mind he feels like he can justify in his mind why he did it."
Sweeney used a manual typewriter and prepaid postcards to send venomous messages to the woman who had argued with him, her husband, and their two adult daughters. The postcards, which were also sent to the victims' workplaces and neighbors, accused the family members of being drunks, sex offenders and racists.
Sweeney hired a private investigator, who Solmon said acted inappropriately by using her personal connections to uncover information about the family members that should not have been available to the public - then passing home addresses and other private details along to Sweeney.
Solmon believes the private investigator had a contact at the Department of Motor Vehicles, enabling her to run the victims' license plates for information.
"That's just a weak link in the system, somebody should not have been providing that information to [Sweeney,]" he said. "One of our victims actually moved out of state, there was a lull for a while, and then when they registered their vehicle again, boom - back on the radar."
The private investigator has not been charged criminally in the case.
The postcards kept coming even after the death of the victim's husband and a move to a new address. Sweeney referenced the victims' real birth dates, addresses, Social Security numbers, and repeatedly warned that he had driven by their house and was monitoring them.
Solmon described the threats as "mental terrorism."
"Like any of us would feel, they felt victimized. They felt threatened," he said. "Not knowing whether this person is actually surveilling their house, following them around, following their children around - giving specific details about their child's school schedule in a whole other state. That's very troubling."
Neither the victims nor investigators could figure out who was sending the postcards.
Solmon said it was clear their then-unknown suspect, whose evasive tactics had left investigators searching for "a needle in a haystack," was very attuned to what law enforcement would be looking for.
"Forensically, it's a nightmare," he said. "They know what they're doing, they've been through the system obviously, they know how this works."
He was right.
Investigators learned later about Sweeney's extensive criminal history, which included wounding a police officer with a machine gun in the 1960s, as well as convictions for mail fraud, obscenity, weapons charges and more.
Sweeney also worked as a mercenary in Rhodesia and was suspected of helping Christopher Boyce - a military contractor convicted of spying for the Soviet Union - flee to South Africa, according to investigators.
"Frank Sweeney is like the real-life fictional character," Solmon said. "What was going on was so crazy that you could hardly believe it, that it actually happened."
It was not until Sweeney got into another argument - this time with a couple at the Wells Fargo bank drive-through window in Garden City in November of 2018 - that law enforcement caught a break in the case.
Sweeney began mailing that couple similar typewritten postcards, as well as sending messages to nearby schools claiming that one of the victims was a convicted child molester.
But unlike in the parking lot quarrel that set off his harassment of the original family, this time, Sweeney had been caught on surveillance cameras at the bank.
Solmon said the team of investigators quickly identified Sweeney as their suspect, then began working on getting a search warrant for his home.
The planned search hit a speed bump early on.
"The day we were going to serve the search warrant, we realized, 'Hey, he's moving,'" Solmon said. "There's a moving truck coming, all these things are happening."
The investigators had to start over and get a different search warrant for Sweeney's new address in South Boise, which they served on March 4.
Inside his home, law enforcement found the typewriter he had used to create the threatening postcards, as well as portraits of Hitler, other Nazi memorabilia, and two live rattlesnakes.
"We were not real happy, because we had to handle those," he said. "I think that falls into the 'other duties as described' part of the job."
Solmon said the Department of Fish and Game refused to take the snakes because they were not indigenous to Idaho and could not be released into the wild. The investigators ultimately got in contact with a reptile collector who had "a house full of snakes" and agreed to take in both rattlesnakes.
Investigators say Sweeney acted surprised that he had been caught, but confessed to stalking the two families immediately.
"He had no qualms about talking about it," Solmon remembered. "I think he's a little bit self-indulgent in that way, that he probably of enjoyed talking about it."
The 76-year-old ultimately pleaded guilty to six felony counts of stalking and was sentenced in December to more than four years in prison.
After years of investigation and moments of doubt about whether the guilty person would ever be caught, Sweeney's arrest and confession was "a joyous moment" for law enforcement, Solmon said.
For the victims as well, he said, the end of the case brought the relief and closure they had been waiting for for so long.
"The guy in the shadows is no longer out and able to do this anymore," Solmon said. "He's confessed to doing this, we know we got the right guy, and now we can go home tonight and have a good night's rest knowing he's behind bars."
The 51-month sentence is near the maximum allowed under the felony stalking statute - and likely much higher than Sweeney would have faced if the charges had been brought in state court, Solmon said. Still, the investigator said, it remains to be seen whether Sweeney will find new victims after his release from prison.
"I suppose he could. It's just a matter of writing a letter, and sending it out," he said. "Hopefully he's gotten to the point where it's not worth it anymore. We'll see - we'll see what happens after 51 months, but if he does, we'll be ready for him."
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