The arrest took place when the suspect showed up at a men's restroom in a remote part of an Elma park, where he had arranged to meet his intended victim, said acting Capt. Rob Huss of the State Patrol.
But instead of an 11-year-old boy, he was met by a detective with the State Patrol's Missing and Exploited Children's Task Force and placed under arrest.
The suspect, identified as Joel R. Alexander, 35, of Snohomish, is a Level II sex offender who was required to register following a 2001 conviction for second-degree child rape.
The case began a few weeks ago when the boy's mother saw inappropriate chat conversations on her son's Facebook account. She notified the Elma Police Department, which in turn sought help from the State Patrol task force.
Detectives then assumed an undercover role, posing as the boy for nearly a month and continuing the online dialogue with the suspect.
During that time the suspect sent child pornography and had graphic online conversations with the supposed 11-year old, Huss said.
During those conversations the two agreed to meet at the specific location in Elma. When Alexander showed up, he was greeted by detectives and taken into custody, Huss said.
Alexander was booked into the Grays Harbor County Jail for investigation of first-degree attempted child rape, communication with a minor for immoral purposes and other possible charges. He is being held without bail.
Detectives later served a search warrant at Alexander's residence in Snohomish and the investigation continues, including identifying any other potential unidentified victims.
The investigation was assisted by the U.S. Marshal's Service Sex Offender Investigations Branch and the Elma Police Department, with support of the Grays Harbor County Prosecutor's Office Huss said.