David Michael Kalac Amber Lynn Coplin Murder Washington
David Michael Kalac, 33, was arrested over the murder of Amber Lynn Coplin Twitter/@WilsonvillePD

A US man accused of killing his girlfriend and posting details of the killing as well as graphic photos of her body online has been arrested in Oregon.

David Michael Kalac, a 33-year-old from Washington, was held by police in the town of Wilsonville, some 20 miles (32km) southwest of Portland.

Clackamas County Sheriff's office tweeted:

Kalac was charged with second-degree murder over the killing of his girlfriend Amber Lynn Coplin, 30.

The suspect allegedly strangled Coplin in her apartment in Port Orchard, Washington, before fleeing with the woman's car.

Police found the word "dead" scrawled over her driving licence that was left next to her body, according to a probable cause affidavit.

The words "she killed me first" and "bad news" were instead written respectively on the bedroom wall and on the window blinds.

Shortly before police were called to the scene, an anonymous user posted photos of Coplin's naked corpse on the online forum 4Chan.

The pictures were accompanied by a message reading: "Turns out it's way harder to strangle someone to death than it looks on the movies."

"She fought so damn hard," the post continued.

The user went on telling other users to check for news in Port Orchard.

"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," the user wrote. "I understand the doubts. Just check the f*****g news. I have to lose my phone now."

Police confirmed that the photos depicted Coplin's body and were most likely posted by Kalac.

"He's our primary suspect," Kitsap County Sheriff's deputy Scott Wilson said. "It stands to reason that in all likelihood he is the person who posted those photographs."

The victim's body was found by her 13-year-old son who then alerted his father - Coplin's estranged husband - who in turn called police.

A manhunt for Kalac ensued. The car he used to flee was found abandoned in Portland, about 160 miles (257km) south of the crime scene.

Police in Wilsonville said he was detained without incident and cooperative. Kalac and Coplin had recently had violent arguments, according to neighbours.