When it was revealed that the Boston Marathon bombers attended a Cambridge, Mass., mosque, its leaders were quick to disavow their actions.

Elder brother Tamerlan Tsarnaev’s ideology was not their own, the leaders of the Islamic Society mosque claimed. In fact, he was admonished for an extremist outburst he made during one sermon.

So, one crackpot in a congregation. Who can blame the mosque?

But what about eight — including a prominent member of ISIS?

As it turns out, worshippers at the Islamic Society have included:

Abdurahman Alamoudi, the mosque’s founder and first president, who in 2004 was sentenced to 23 years in prison for plotting terrorism. In 2005, the Treasury Department issued a statement saying Alamoudi raised money for al Qaeda in the US.

Aafia Siddiqui, an MIT scientist-turned-al Qaeda agent, who in 2010 was sentenced to 86 years in prison for planning a New York chemical attack. Known as “Lady al Qaeda,” she is related to 9/11 mastermind Khalid Sheik Mohammed. ISIS has tried to trade her release for journalist hostages.

Tarek Mehanna, who in 2012 got 17 years in prison for conspiring to use automatic weapons to murder shoppers in a suburban Boston mall.

Yusuf al-Qaradawi, a mosque trustee and Egyptian Muslim Brotherhood leader banned from the US after issuing a fatwa that called for the killing of US soldiers.

Jamal Badawi, another former trustee who in 2007 was named an unindicted co-conspirator in a plan to funnel more than $12 million to Palestinian suicide bombers.

Now it can be revealed that another regular worshipper at the Islamic Society mosque was Ahmad Abousamra, who is now the top propagandist for ISIS.

Abousamra’s father, a prominent doctor, even sat on the board of directors of the Muslim organization that runs the mosque. He stepped down after the FBI began questioning his son.

The FBI suspects Abousamra now operates ISIS’s sophisticated media wing promoting the group’s beheadings and other atrocities through slick videos posted on the Internet. The brutally effective English-language propaganda campaign has helped attract thousands of Western jihadists, including at least 300 Americans.

The FBI says Abousamra, 32, traveled to Pakistan and Yemen to train to kill Americans while enrolled at Boston colleges. He justified murdering civilians because “they paid taxes to support the government and were kufar [nonbelievers],” Boston FBI Agent Andrew Nambu testified in an affidavit.

Another agent, Heidi Williams, says Abousamra, who has a $50,000 bounty on his head, was inspired by the 9/11 attacks and, in fact, “celebrated it.”

A federal indictment says he even plotted to randomly gun down shoppers, then emergency responders, in a Boston mall. But when he couldn’t obtain the automatic weapons for the attack, he abandoned the plan and moved to Syria, where he could enter Iraq and kill US soldiers as part of “violent jihad.”

Where did he learn his views about Islam and jihad?

The Islamic Society insists it’s moderate — that these extremists were fed by online forums. But Charles Jacobs, head of Boston’s Americans for Peace and Tolerance, says the mosque has hosted pro-jihad speakers and has stocked its library with classic jihadi texts — including writings by Osama bin Laden mentor Syed Qutb.

And Islamic Society leaders have openly defended their worshippers convicted of terrorism — including Siddiqui and Mehanna — despite overwhelming evidence against them. At their hearings and trials, officials have sought their release or lenient sentences. They have also held fundraisers and rallies for the terrorists.

Recently, investigators found a mosque prayer card for Mehanna tucked in a Russian dictionary in Tsarnaev’s Cambridge apartment.

Abousamra’s father, Dr. Abdulbadi Abousamra, was president of the Islamic Center of New England mosques until 2007, when he moved to Detroit. The FBI began questioning his son a year earlier. As mosque president, internal documents show, Dr. Abousamra hired Hafiz Masood, brother of a known Pakistani terrorist, to be the imam of a mosque in Sharon, Mass., which his son also attended.

Dr. Abousamra, now chief of endocrinology at Wayne State University in Detroit, did not return emails and phone calls seeking comment.

As for the Islamic Society, it insists it isn’t preaching hate.

But how many terrorists does it take before people are convinced it isn’t a coincidence?

Paul Sperry is a Hoover Institution media fellow and author of “Infiltration: How Muslim Spies and Subversives Have Penetrated Washington.”