Kwang Chol Joy, 54, was arrested Friday, the Los Angeles Times reported. Investigators said he came in voluntarily for a police interview.
Maribel Ramos, 36, was about to graduate from Cal State Fullerton. She was reported missing May 3, and had been scheduled to speak at a veterans' event but failed to show up.
Her body was discovered Thursday in a ravine in an unincorporated area in Orange County.
Someone using the name "KC" posted on Yelp Monday, describing Ramos as his "BFF." The post mingled complaints about the police investigation with mourning for Ramos, the newspaper said.