LOS ANGELES — The news made Nihad Awad sick to his stomach.

Like the rest of the nation, Awad, who heads the Council on American-Islamic Relations in Washington, learned this week that it was a Muslim who opened fire at Fort Hood, a U.S. Army base in Texas, killing 13 people and injuring many more.

According to soldiers, Army Maj. Nidal Malik Hasan allegedly issued the cry of his faith before opening fire: "Allahu Akbar!" ("God is great.")

Hearing the story, Awad, too, would invoke his maker – but with a weary lament that is echoing coast to coast among moderate American Muslims.

"I said, 'Oh God, here we go again,' " recalled Awad. "We know what will come when a Muslim name flashes across the (television) screen. What will come is guilt by association."

In the wake of Thursday's shooting, mosques around the country Friday denounced the violence and implemented a range of overt and subtle security measures. In Los Angeles, Islamic groups contacted police and sheriffs, who stepped up patrols of mosques and community centers.

Janan Al-Henaid, a sophomore at the University of Southern California, got a call from her mother Friday asking her to come home to Claremont and to be careful when going out.

"And she's never done that before," Al-Henaid said.

A number of Muslim groups participated in a conference call Friday with federal agencies – including the Department of Homeland Security and the Justice Department – to discuss Muslim Americans' safety.

Eight years after the Sept. 11 terrorist attacks, mainstream Islam remains a subject of suspicion to some Americans – a perception perhaps fueled by prejudice and fear, but also by recent reports of broken-up terrorist plots hatched by homegrown Muslim radicals. Despite eight years of post-9/11 education campaigns, the suspicion and the scrutiny remain a source of deep frustration for Muslim American leaders.

Salam Al-Marayati, executive director of the Muslim Public Affairs Council in Los Angeles, said the massacre would be exploited "by groups like al-Qaida, that will use it as a card to justify more religious extremism and violence, and by Muslim haters – who will use it to divide our country and foment fear and hatred."

Al-Marayati said he first prayed for the victims. Then he offered another prayer.

"We prayed," he said, "that it was not a Muslim."

Hasan, a Virginia-born psychiatrist, was in many ways a product of the American mainstream. But among some observers, the rampage stoked long-standing fears about the divided loyalties of even moderate Muslims. The right-wing news site WorldNetDaily argued that Hasan was "just the tip of a jihadist Fifth Column operating within the ranks of the U.S. military."

Lt. Col Lee Packet, an Army spokesman, called the assertion "total speculation."

Muslim community leader Maher Hathout addressed such fears in an emotional sermon at the Friday at the Islamic Center of Southern California. Speaking to 2,000 worshippers, Mathout said a caller had posed a question: Could any Muslims be trusted now?

"This is the question on the minds of your co-workers, on the minds of your neighbors – this is the trust, and we have to do something about it," he said.

Hathout implored them not to hide from the aftermath of the shooting but to speak about any lingering misperceptions with their neighbors.