WASHINGTON — An anti-Muslim activist who tipped an Egyptian newspaper reporter to the existence of an incendiary anti-Islam video, setting off a chain reaction that climaxed in the storming of the U.S. Embassy in Cairo last week, has dropped from sight.

Morris Sadek, 69, last posted to his Twitter account on Sept. 10, the day before violent protests broke out over the crude 14-minute YouTube clip, “Innocence of Muslims,” which depicts the Prophet Muhammad as a cartoonishly evil child molester and killer.

Sadek’s Facebook account is offline, and his website hasn’t been updated in a week.

Neighbors in Chantilly, Va., say they haven’t seen Sadek or his family since Thursday. No one answered the door of his two-story brick townhome on Monday, although someone had collected notes and business cards left by reporters on Thursday, along with a package delivered the same day by the U.S. Postal Service. A light was on in the front hall but no movement could be detected inside the house.

Sadek is most likely in hiding, fearful for his life, said Magdi Khalil, spokesman for Coptic Solidarity, a nonprofit human rights organization based in Washington.

Khalil said Sadek is well known among Copts for his anti-Muslim acts. “He is just somebody . . . who just wants to make the Muslims angry. He insults the Muslims weekly," Khalil said.

On his website, Sadek identifies himself as a human rights attorney and president of the National American Coptic Assembly. Records show the assembly was incorporated in Virginia in 2001. Its address is Sadek’s home in Chantilly, a Washington suburb.

Khalil said the assembly has little influence. “Just a name and a few members,” Khalil said.

Coptic Christians are a religious minority in Egypt, where they make up about 10 percent of the population. Sadek was widely viewed there as a troublemaker, and his Egyptian citizenship was revoked in 2011 for "calling for war against Egypt," among other crimes, according to Cairo’s Egypt Independent newspaper.

This time, Sadek’s efforts to provoke Muslims had dire consequences. He persuaded an Egyptian newspaper reporter to write about “Innocence of Muslims,” and the story got picked up by blogs, other newspapers, and finally a popular television station with ties to the conservative Salafist strain of Islam, which aired a segment of the video on Sept. 9, two days before the embassy attack. Demonstrators infuriated over the insult to Islam then attacked U.S. embassies across the Middle East, with the outburst reaching its crescendo on Friday, when protests took place in at least 23 countries.

The film’s alleged creator, a 55-year-old convicted felon named Nakoula Basseley Nakoula, also appears to have fled his home in Cerritos, Calif.

Khalil said Nakoula called him to ask his advice after the video hit the headlines. He claimed to have met Khalil at a lecture in California. Khalil says he doesn’t remember the man but tried to help him for the sake of his family.

“He called me many times,” Khalil said. “I told him ‘Leave your home immediately. I’m worried about your life. I’m worried about your kids and your wife. So please leave and don’t speak to anybody.’”

Khalil said all Copts now fear that they will face a backlash because of the actions of a few extremists in their community.

“We are against Morris Sadek,” Khalil said. “He didn’t do anything for Copts, just for himself to be famous.”