Episode 72:
The Killer’s Mark: Solving a Cold Case Through a Unique Signature

A predator who targeted women living alone, carrying out robbery and sexual assault. But this was just the tip of the iceberg. He used his own signature method when binding his victims — and the police intuitively knew he was no ordinary criminal.

Even more shocking, a search of his home revealed over seventy wristwatches hidden in a drawer. Just how many people did he target?

At 7:30 a.m. on March 11, 2012, a call came into the Seongbuk Police Station in Seoul, traced to a payphone in Dongseon-dong: "Please help me. Someone broke into my home. I was sexually assaulted. He took my gold necklace. Please come quickly — he might come back."

An Unlocked Door

Officers found the caller, 23-year-old university student Kim A-yeong, hiding in a phone booth fifty meters from her studio apartment. She'd come home exhausted the night before and forgotten to lock her door properly — a mistake she'd remember for the rest of her life. She woke to a masked man, roughly 180 centimeters tall, shaking her awake. He unplugged her phone, rifled through her wallet's meager $23, and tore the gold necklace from her neck before deciding to stay.

He taped her eyes and mouth and bound her wrists with cable ties in a distinctive method: forcing her hands together while isolating and separately binding only her thumbs and pinkies. Investigators recognized it immediately as something more than convenience — a criminal signature, the kind that develops through repeated offenses as a method gets refined and reused. This wasn't a first crime.

A DNA Match to a Cold Case

The scene itself was clean — no prints, no footprints — but the attacker left his DNA. With the victim's consent, investigators ran it through the national forensic database, and the result reopened an unsolved case from two years earlier: a 99.9% match to the suspect in the Suyu-dong rape, murder, and arson case.

In July 2010, a fire had engulfed a multi-family villa in Suyu-dong, killing 24-year-old Ms. Lee on the third floor. Her body, badly burned, showed she'd been strangled and sexually assaulted before the fire — duct tape remnants on her face, and the same distinctive binding method: only her thumbs and pinkies restrained with cable ties. Her killer's DNA had been recovered at the time, but with no database match and every acquaintance cleared, the case had gone cold.

The Cardigan and the Transit Card

Back on the Dongseon-dong case, with no witnesses at that early hour, police pulled footage from over a hundred nearby cameras — guided by one detail A-yeong had noticed before she was blindfolded: a grey knit cardigan with white snowflakes. Frame by frame, they found their man walking calmly toward Miari Hill before vanishing from camera range — meaning he'd switched to public transit.

He made two mistakes. His transit card recorded his exact route — bus past Sungkyunkwan University, subway from Hyehwa to Suyu Station, another bus toward Ssangmun Bridge — and he removed his mask entering the subway, giving police a clear face for a sketch. Cross-referencing his transit pattern (out at 6 a.m., back at 7 p.m., consistent with a daily commute) against footage from shops near his likely home base, they caught him on camera at a local mart — signing up for a rewards card with his real name and phone number.

"She Didn't Get a Look at My Face"

The man was 37-year-old Kang, working by day as a special security officer — quasi-police personnel stationed at banks and public institutions. A juvenile robbery conviction from his teens had never been formally registered, letting him pass every background check clean. On March 20th, surveillance teams spotted him near Suyu Station; confronted, he answered calmly: "I know why you're here. It's because of that case two years ago, and the recent one."

He confessed readily, citing credit card debt and stress, and claimed he'd learned the binding technique from television. The two-year gap, he said, came from crippling sleep paralysis after the Suyu-dong killing — convinced the victim's spirit was haunting him, he slept with a knife under his pillow and eventually decided that committing another crime, killing his guilt along with it, might make the nightmares stop. Asked why he'd let A-yeong live when he'd murdered before, his answer was chillingly practical: "She didn't get a look at my face" — and he assumed shame would keep her silent, just as two years of police silence had convinced him he was untouchable.

Final Thoughts

A-yeong proved him wrong immediately, calling police the moment he left and giving investigators everything they needed. A search of Kang's home turned up 78 wristwatches, nearly half of them women's, along with 13 knives. He claimed the watches were scavenged from empty redevelopment-area homes meant for resale — an explanation that didn't sit well with anyone, given he'd never sold a single one. Police suspected additional undiscovered victims but, with Kang refusing to say more and no further evidence surfacing, could only charge him for the two confirmed cases: murder, aggravated robbery, aggravated rape, and arson. He was sentenced to life in prison.

The case came together through nothing more exotic than a cardigan pattern, hundreds of hours of camera footage, a transit card log, and a supermarket rewards signup — routine conveniences that turned into the evidence that finally connected two years and two crime scenes. Ms. Lee's family got an answer they'd waited two years for, and Kim A-yeong's decision to run, hide, and call police the moment she had the chance meant Kang never got the chance to test how far he'd go next.