A criminal complaint filed Thursday against Enrique Marquez marked the first charges — and the first arrest — produced by the sprawling investigation into the Dec. 2 attack in San Bernardino, Calif.

While the complaint was largely focused on Marquez’s statements and the allegations against him, the 36-page affidavit filled out by an FBI agent also offers the most insight available yet into Syed Rizwan Farook, who authorities say went with his wife to a holiday gathering and killed 14 people.

The complaint is full of new details about Farook’s background and influences, information that the FBI learned from a series of interviews with the 24-year-old Marquez.

The document paints a picture of Farook, 28, as a young man who spent years steeped in extremist thought easily accessible online. He is described as hoping to travel to join a terrorist group and, with Marquez, plotting to carry out attacks here.

Much of the affidavit focuses on the level of planning and preparation that went into attacks Farook and Marquez plotted to carry out in 2012. Investigators say the two men scouted locations — picking a community college both had attended and a busy state road as their targets — and went on to visit firing ranges for target practice, buy firearms and purchase materials for explosives.

It also says that Farook’s discussions and plotting occurred as long as four years before the San Bernardino attack, predating both his contact with his future wife, Tashfeen Malik, and the formal declaration of the Islamic State.

After the mass shooting in San Bernardino, Calif., on Dec. 2, details are starting to emerge about who was involved in the attack. (The Washington Post)

Farook was born in Chicago in 1987 to Pakistani parents and has been described as a seemingly happy, quiet and deeply religious man, one who displayed no warning signs to co-workers or neighbors.

But according to the affidavit, Marquez told investigators that Farook was exposing him to extremist views and ideas years ago. The two became neighbors a decade ago, and not long after, Farook introduced Marquez to Islam. By 2007, Marquez had converted to the religion and Farook then “introduced Marquez to radical Islamic ideology,” FBI Special Agent Joel T. Anderson wrote in the affidavit.

Farook is presented in the affidavit as the force pulling Marquez toward violent extremism. At one point, Marquez said, Farook told him he was interested in joining al-Qaeda in the Arabian Peninsula, which the United State has designated a terrorist group.

Farook also introduced Marquez to the lectures of Anwar al-Awlaki, a U.S.-born imam who inspired numerous terrorist attacks and was killed in a 2011 drone strike. Awlaki left behind a considerable digital archive, and authorities said videos of his lectures were also viewed by the man who killed five people at military facilities in Chattanooga, Tenn., earlier this year.

After Army Maj. Nidal M. Hasan opened fire in 2009 on a group of soldiers at Fort Hood, Tex., killing 13 people, Farook “expressed disdain toward Muslims in the military who killed other Muslims,” Anderson wrote.

In 2011, Marquez said he spent much of his time at Farook’s home, consuming a steady diet of extremist thought. The men watched videos produced by al-Shabab, the Islamist terrorist group affiliated with al-Qaeda, and read Inspire, al-Qaeda’s English-language magazine.

That same year, Marquez and Farook began discussing how to use guns and explosives to carry out attacks “designed to maximize the number of casualties that could be inflicted,” Anderson wrote.

Farook and Marquez never attempted to carry out these earlier plans. Marquez told investigators that he stopped plotting with Farook and distanced himself from him after a terrorism investigation in Riverside ended with four local men arrested in November 2012 for plotting to kill Americans in Afghanistan. These men were later convicted and sentenced to prison.

It was not until late the following year that Farook was corresponding with Malik, who would become his wife, about martyrdom and jihad, according to FBI Director James B. Comey. Investigators have found no evidence that Farook had any connections to those men nor any any ties between Farook, Malik and any other organizations, according to Comey.

President Obama on Friday defended the work of U.S. law enforcement, noting that recent allegations that they had overlooked social media activity by Malik were incorrect. The New York Times had published a story saying that Malik had publicly expressed sympathy for violent jihadists on social media. On Wednesday, Comey dismissed that report and said she had sent private messages.

In a news conference, Obama acknowledged that there was no real way for U.S. authorities to guarantee attacks like the one in San Bernardino would not happen again.

“It is very difficult to detect lone-wolf plots, and plots by a husband and wife,” Obama said. “It’s not that different from us trying to detect the next mass shooter. You don’t always see it.”

The plots Farook and Marquez discussed in 2012 reached a high level of detail, according to the complaint. In their plan to attack Route 91, they discussed throwing pipe bombs into the road to stop traffic, the FBI alleges. Authorities say one of them planned to fire into the stopped cars, while the other would climb a nearby hill and shoot at the police officers and emergency responders who arrived, with a particular focus on killing law enforcement officers.

In another plot, the men discussed going to Riverside City College, a community college both had attended, and throwing pipe bombs into the cafeteria before attacking another location.

Authorities also said that in addition to buying the guns used by the husband-and-wife attackers, Marquez bought explosive material later used to construct the pipe bomb that authorities found at the Inland Regional Center after the mass shooting.

The most serious charges pertain to the earlier plots from 2012 rather than the San Bernardino shooting. But Marquez was also charged with making a false statement in connection with the acquisition of firearms used in that attack.

Marquez bought two assault rifles for Farook in 2011 and 2012 so that they could be used in their 2012 plot, he told investigators. Marquez went on to sign forms stating that he was buying them for himself, but the government alleges they were a straw purchase.

“While there currently is no evidence that Mr. Marquez participated in the Dec. 2, 2015, attack or had advance knowledge of it, his prior purchase of the firearms and ongoing failure to warn authorities about Farook’s intent to commit mass murder had fatal consequences,” U.S. Attorney Eileen M. Decker of the Central District of California said in a statement.

The complaint also states that hours after the shooting, Marquez called 911 to report that Farook, his former neighbor, had used his gun in the attack.

“My neighbor. He did the San Bernardino shooting,” Marquez told the 911 operator. “The f—ing asshole used my gun in the shooting.”

These details about Marquez’s interactions and history come from a series of interviews the FBI conducted with him over an 11-day period, beginning four days after the shooting and continuing through Wednesday, the day before Marquez was charged.

Marquez waived his right to have an attorney present each day he was interviewed, the affidavit states. Some of the details in the affidavit are not independently verifiable, given that they involve conversations Marquez had with Farook; in some cases, the FBI used things like bank records to confirm information and figures Marquez described. 

On Thursday, the day he was arrested, Marquez made his first court appearance in Riverside, Calif. It was the first time he was seen publicly since becoming the focus of the investigation.

He seemed relaxed, leaning back in his chair, and said he understood the charges against him.

Horwitz reported from San Bernardino. Adam Goldman, Ellen Nakashima and Julie Tate contributed to this report.

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[This story has been updated.]