EVERETT — For 23 years detectives have wondered if the person who sent rambling, taunting letters to the families of a slain Canadian couple was the killer or just a kook.

Last week, shortly after releasing new details about the letters, detectives got their answer.

Tips from the public, and old-fashioned street-pounding police work led homicide detectives to a mentally ill Canadian man who admitted he was the author of the hurtful correspondence.

In the letters, the man claimed that he killed Jay Cook and Tanya Van Cuylenborg. He bragged he’d never be caught and threatened to kill again if he got the opportunity.

Detectives don’t believe the letter writer, now in his 70s, is responsible for the 1987 slayings.

“He’s not a suspect. He denies involvement, and nothing links him to the crime scenes,” Snohomish County sheriff’s Detective Jim Scharf said. “Now we can focus our attention on who actually did kill the young couple.”

Cook, 20, and Van Cuylenborg, 19, had traveled from British Columbia to Seattle to run an errand for Cook’s father.

Van Cuylenborg’s body was discovered Nov. 24, 1987, south of Alger in Skagit County. She had been sexually assaulted and shot. Cook’s body was found two days later under High Bridge off Crescent Lake Road in Monroe. He’d been strangled and asphyxiated.

The killer abandoned Cook’s van in a downtown Bellingham parking lot. Some additional evidence was found under the back porch of a bar near the city’s bus station.

Investigators believe the killer came prepared with a kit, likely containing a gun, zip ties, gloves and other tools, Skagit County sheriff’s Detective Tobin Meyer said. Police believe the suspect picked the couple at random, likely crossing paths with them in downtown Seattle.

A week after the killings the letters began showing up.

The man who admits writing to the families provided police a genetic sample, which they will have compared against the DNA recovered from the letters. Tests recently showed that the DNA profile from the letters doesn’t match other forensic evidence collected at the scene where Van Cuylenborg’s body was discovered.

That information led police to believe the letter writer likely wasn’t the killer. They were ready to share the details of the letters with the media to solicit tips from the public in hopes of tracking down the letter writer.

Pieces of the puzzle quickly began to fall into place.

First, a person in Canada saw a story about the letters on “Washington’s Most Wanted,” a weekly television show on KCPQ-TV that features cold cases. The man recognized the handwriting from the letters and contacted police. An anonymous caller then left the name of the man with Snohomish police, who passed the information along to the sheriff’s office.

The man’s name is common. Police needed more to pick up the trail. They searched the database of names that Skagit County detectives built for the case. They located the man’s name, along with a date of birth in the case files.

Scharf said the man’s name was added to the case file during the initial investigation into the letters. In one of the letters, the author mentioned writing to true-crime author Ann Rule, of Renton. Early in the investigation, detectives contacted Rule, who gave them a possible source of the letters, a man who’d written her, Scharf said. In the letters to Rule, he’d signed his name.

“Oftentimes in these cold cases the name is the file,” Scharf said.

Police used all the information to determine that the letter writer was a transient who roamed between Canada and Washington state. Canadian authorities tracked his last known address to a homeless shelter in east Vancouver, B.C. He hadn’t been there in eight months. Detectives followed more tips and tracked him to another location in Washington, where he’d been seen two weeks earlier.

Then they learned he’d been at another place the day before.

They set up surveillance. Investigators walked up to the man Aug. 20 at a location in Western Washington. Police declined to say where.

The man, who has lived on the streets for decades, was apologetic, Scharf said. He told detectives he once called Cook’s father with the intention of apologizing but didn’t reach the grieving man. He lost the nerve to try again, Scharf said.

“He said it was horrible, a stupid thing to do,” Scharf said.

The man, who police declined to name, told investigators that he’d read about the murders in the days after the victims’ bodies were discovered. He was at a low point in his life and wanted to lash out, Scharf said.

Born and raised in Canada, he was angry about how he’d been treated by his fellow Canadians. He already was an avid letter-writer. He mailed letters and cards to the families for a year.

The statute of limitation is up and the man isn’t expected to face any harassment charges connected to the letters, Scharf said.

The man on Tuesday traveled to the sheriff’s office to speak with Scharf. The detective wasn’t in the office. The man left a letter, Scharf said.

News that investigators caught up with the letter writer was bittersweet for the victims’ families, Meyer said.

“This a big chunk of the mystery, but it didn’t resolve the case because we still don’t know who the killer is,” Meyer said.

Detectives received an anonymous tip from someone who read about the letters in The Herald earlier this month. The tipster gave a name of someone he or she suspects is responsible for the killings. Police are hoping the person will call them back so they can ask additional questions.

“This person’s information might be good. We don’t know,” Scharf said.

He said it’s difficult to track down anonymous tips. Information is more beneficial if detectives can ask questions of the tipster.

“We often need to ask a lot more questions,” Scharf said. “We can’t get that information if we can’t contact people.”

Diana Hefley: 425-339-3463; hefley@heraldnet.com.

Help detectives

Anyone with information about the 1987 slayings of Tanya Van Cuylenborg and Jay Cook is asked to call the Snohomish County sheriff’s tipline at 425-388-3845. Tipsters are encouraged to leave a return phone number for detectives.