EVERETT — She was a young teacher preparing for summer classes at Discovery Elementary School in south Everett when he broke into her classroom, pointed a gun at her and ordered her on the floor.

He took $14 from her purse and demanded her jewelry. She handed over her wedding ring. He gave the ring back and then raped her. The suspect threatened to shoot her, ripped the phone from the wall and fled the portable classroom.

That was 1998.

Sheriff’s detectives on Wednesday arrested the man they believe is responsible for the attack. Investigators say advances in forensic testing in the last decade led them to the Everett man, now 30.

The suspect was 17 at the time and lived less than a mile from the school. He was a high school dropout and had been in trouble with the law before that summer, including juvenile convictions for property crimes.

The victim told detectives at the time that the attacker wore gloves, a black stocking cap and something covering his mouth. She estimated that he was in his late teens or early 20s.

A police dog searched the area. Investigators concluded that the suspect likely fled on bicycle.

Detectives speculated that the attacker knew that the woman was working alone in the classroom, entered through an open window and waited for her to return from lunch.

“I think he planned this. He was dressed all in black. He wore a scarf or something over his face and was carrying a handgun,” sheriff’s cold case detective Jim Scharf said.

The detective helped process the crime scene that day.

Forensic evidence collected during the investigation was tested at the time but didn’t lead to any suspects.

In June, Scharf contacted a forensic scientist at the Washington State Patrol crime lab in Marysville and asked if there was enough genetic evidence that could be retested using today’s more advanced technology.

He and the other cold case detectives have been re-examining evidence in old unsolved homicides to determine if new forensic testing should be done. This case came to mind, Scharf said.

“This is a pretty horrific case,” he said. “You don’t forget about the really bad ones.”

Scientists conducted the tests, and discovered a match with the evidence collected and a sample in the state’s DNA database.

Since the rape, the suspect was twice convicted of burglary and a suspect in a string of 60 break-ins in Snohomish County in 2000. He was required to submit DNA samples after those convictions. The information was entered into the state’s database.

Detectives arrested the man Wednesday and booked him for investigation of first-degree rape and burglary. He was on parole for a federal conviction stemming from a string of pharmacy burglaries along the West Coast, sheriff’s spokeswoman Rebecca Hover said.

Investigators on Wednesday collected a fresh DNA sample from the suspect. That will be tested against the evidence collected in 1998.

The sheriff’s office received a nearly $400,000 federal grant in 2009 to bolster its cold case investigations. The sheriff’s office added two more detectives to the squad. Investigators have been identifying items to be tested for potential DNA and submitting that evidence to the state crime lab.

“I credit the tenacity and dedication of detective Scharf and his cold case colleagues for bringing about justice in this case – both for the victim and all citizens of Snohomish County,” Sheriff John Lovick said.

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