ALAMEDA --An Alameda man faces multiple felony charges after he blackmailed a former girlfriend into continuing a sexual relationship with him by threatening to post explicit video footage online that he had secretly recorded of them together, police say.

Investigators are now reviewing computer hard drives and other evidence that they seized at the Santa Clara Avenue home of Phuc Thien Nguyen, 38, who was arrested Tuesday and booked on suspicion of rape and other charges.

Nguyen met the victim about four years ago when they were both attending Laney College in Oakland, Alameda police detective Sgt. Wayland Gee said.

Nguyen is suspected of pressuring the 21-year-old victim, whose name was not disclosed, into repeatedly having sex, including after they ostensibly had broken up, according to investigators.

It was not immediately clear when the woman, who lives in San Francisco, initially attempted to end the relationship. But Nguyen routinely e-mailed and texted her, including sending screen shots that showed them intimately together, Gee said.

The victim told police she did not know about the existence of the images until Nguyen began sending them.

"He used them to threaten her," Gee said. "He said he would post video online and embarrass her and her family unless she continued to have sex with him."

The victim contacted police Tuesday, saying Nguyen had grabbed and choked her during an argument.

While officers were questioning her, however, they learned about the alleged blackmail, which prompted investigators to secure an arrest warrant for Nguyen and a search warrant for his residence.

Reach Peter Hegarty at 510-748-1654 or follow him on Twitter.com/Peter_Hegarty/.