Photos of body online; man arrested

• Suspect arrested near Portland


• David Michael Kalac, 33, is accused of killing his girlfriend, Amber Lynn Coplin


• "Outside of a terrorist attack this is as serious as you can get," an official says

(CNN) -- Oregon authorities have arrested a man accused of killing his girlfriend in Washington state and posting gruesome pictures of her body online.

David Michael Kalac, 33, was taken into custody near Portland late Wednesday by the Wilsonville Police Department.

He was wanted on suspicion of second-degree murder.

"Outside of a terrorist attack this is as serious as you can get," said Deputy Scott Wilson of the Kitsap County Sheriff's Department.

Authorities first received a call Tuesday afternoon. When they arrived at the apartment in Port Orchard, Washington, they found the body of Amber Lynn Coplin, 30.

Around the same time, authorities started receiving tips about suspicious photographs posted online on social media sites Imgur and 4chan.

"The initial poster, believed to be Kalac, was also posting comments with the pictures. He said that the crime scene would be discovered and what he was going to do. We took this very seriously. We have no reason to believe that anyone posted them but him," the deputy said.

According to CNN affiliate KOMO, the statement read, in part: "Check the news for Port Orchard Washington in a few hours. Her son will be home from school soon. He'll find her, then call the cops. I just wanted to share the pics before they find me. I bought a BB gun that looks realistic enough. When they come, I'll pull it and it will be suicide by cop. I understand the doubts. Just check the (expletive) news. I have to lose my phone now."

KOMO reported the same writer later added: "Turns out its way harder to strangle someone to death than it looks on the movies. She fought so Damn hard."

Kalac has a history of domestic violence and making threats to law enforcement, Wilson said.

The victim's missing vehicle was found abandoned in Portland earlier in the day.

CNN's Tony Marco, Tina Burnside, Dave Alsup and Amanda Watts contributed to this report.