EVERETT — At the time Tyler Sullivan went missing, his girlfriend was going on eight months pregnant.

The baby came 1½ weeks early.

Sullivan never came home.

In November, the girl celebrated her sixth birthday, days after authorities figured out what became of her father.

A land surveyor found the human skull in the woods on the Tulalip Reservation in 2016. Three years passed before clues in his family tree, uncovered by a genealogist, helped investigators to confirm the identity of the remains.

Dental records showed the skull belonged to Sullivan, the Snohomish County Medical Examiner’s Office announced Friday.

How he died remains a mystery.

Sullivan lived in the Tukwila area in 2013, but he grew up in north Snohomish County. His friends and family still live around Marysville. He met his girlfriend at the time, Ileana Gonzalez, now 32, by working shifts with her at Chipotle on Third Avenue in Seattle.

Gonzalez knew nothing about his past life behind bars, for heroin possession, theft and other crimes, she said.

“They’d been together maybe a year, but he loved her, and he wanted to do so much so differently,” said his sister Tosha Chrobak, 38. “He didn’t want her to know about all his wrongdoings. He wanted it to be for him, not to be judged because of his past.”

A dark running joke in his family had been, “What is it you like about prison so much?”

In early fall 2013, he disappeared for a little while — until Chrobak told Sullivan’s girlfriend to check in with jails.

“She started telling me all these things,” Gonzalez said. “It’s a lot to process. Obviously I didn’t know where to look. We found out he was at the SCORE (jail) in Tukwila.”

She picked him up three days later. He vanished again in late October 2013, at age 26. His sister suspects he slipped back into the world of drugs. Gonzalez said she heard from someone who worked at a Money Tree in downtown Seattle that Sullivan ran into the business that month, soaking wet but only from the neck up, saying someone was chasing him. Then Sullivan ran off.

In the days that followed, Gonzalez got texts from weird phone numbers. Some were threats from strangers. Others claimed to be from Sullivan, wanting to see her. Eventually it all went quiet. She wondered if Sullivan just needed time away. Both Gonzalez and Chrobak said he had issues connecting with people because of childhood trauma.

“He never had a chance, to put it bluntly,” Chrobak said. “He went to prison for drug use, but everybody just loved Tyler, because he was a sweet kid. … My dad was always there for him, even if it was enabling him.”

His sister figured he’d show up on their dad’s doorstep, looking for cash or help. Or else he’d get in legal trouble, because it wasn’t like him to go more than a few months without some run-in with the cops. Neither of those things happened. Chrobak reported him missing in March 2014.

“I get that he’s got a history, and that most people would presume what is happening or would have happened, but there’s just things that I know with every fiber of my being, that Tyler didn’t want to be missing,” she said. “Something was wrong. Something happened to my brother.”

On a Facebook page, “Find Tyler R. Sullivan,” relatives pleaded with the public to stay vigilant.

“Tyler has been MISSING for a year,” one post read. “His family (members) search for answers and hold onto hope.”

One year turned into another.

Meanwhile, a sun-bleached skull with four upper teeth and no jawbone was found May 16, 2016, among swampy trees along 116th Street NE, east of Quil Ceda Boulevard. The Daily Herald ran a short article on the discovery.

Carlos Echevarria, then-chief of Tulalip Tribal Police, told media that “further tests (were) required to determine whether the skull is, in fact, human.”

Tribal detectives called the FBI to help search for any other remains. None were found. Investigators suspected the skull came from somewhere less exposed to the elements, but it’s unclear how it was moved. There were no signs of trauma, at least to the recovered part of the cranium.

“As this is an open investigation, no further comments will be issued until close of inquiry,” the Tulalip police chief said in a statement in 2016.

And with that, the case of the Quil Ceda John Doe went out of public view for years.

Forensic anthropologist Dr. Kathy Taylor determined the skull came from a grown man with European ancestry.

In 2018, the case was reassigned within the FBI. Police combed the woods again with dogs. Forensic artist Natalie Murry reconstructed traits of the man’s face based on the skull. Small samples of bone were sent to labs for DNA extraction and analysis. Two teeth gave a usable genetic profile to a lab, DNA Solutions. It was posted to the public ancestry website GEDmatch, in search of relatives who had shared the fingerprints of their DNA online.

Investigators’ newfound use of genetic genealogy has led to breakthroughs in long-unsolved homicides and mysterious deaths nationwide. Authorities in Snohomish County became the first to step into a new forensic frontier last year, when William Talbott II was arrested, tried and convicted of murdering a Canadian couple in 1987, with the help of a genealogist and DNA from a crime scene.

In noncriminal cases, genealogists have helped the Snohomish County Medical Examiner’s Office to restore names to a man found dead by suicide in Yost Park in 2018; a piece of shattered human skull caught up in the Skykomish River in 2017; and a skeleton unearthed near Lynnwood in 1978.

Genealogist Barbara Rae-Venter, whose celebrated work on the Golden State Killer case landed her on Time Magazine’s 100 Most Influential People list in 2019, took on a key part of the Quil Ceda investigation. Rae-Venter and her team volunteered well over 50 hours to track down names of people who shared a significant percentage of DNA with the skull. She built family trees, until investigators got in touch with a Georgia man. He knew a family member in Washington state who was missing a relative.

The missing man turned out to be Tyler Sullivan, who was known to hang out near the Tulalip Resort Casino, hardly a mile from where the skull was found. Family members were asked to submit DNA samples to compare.

In the meantime, forensic dentist Dr. Gary Bell examined records of Sullivan’s teeth alongside those in the skull in late October 2019, and found them identical to the point that the DNA testing did not need to proceed.

“It was shocking,” Gonzalez said, “because I really had hopes for something different. I just thought a lot about how we can all make different decisions in our lives. He was not a bad person. … He was trying his best, to stick to the goals he had.”

The cause and manner of death remain undetermined.

Caleb Hutton: 425-339-3454; chutton@heraldnet.com. Twitter: @snocaleb.

The investigation is open. Tips can be directed to Tulalip Tribal Police at 360-716-4608, Tulalip detective Sgt. Wayne Schakel at wschakel@tulaliptribalpolice.org, or the FBI at 800-CALL-FBI.