The ties between San Bernardino mass shooter Syed Rizwan Farook and his shy, younger neighbor ran deep long before last week's massacre at the Inland Regional Center.
Enrique Marquez spent countless hours next door tinkering on old cars in the driveway of Farook's Riverside home. Marquez converted to Islam, Farook's religion, and made trips to pray in a local mosque. He married a member of Farook's extended family, a Russian emigre.
And ultimately, federal authorities say, Marquez bought the two assault-style rifles Farook and his wife, Tashfeen Malik, used in the worst terror attack on U.S. soil since Sept. 11, 2001.
Farook, 28, and Malik, 29, were killed in a gun battle with police shortly after the shootings.
The next day, Marquez posted a cryptic message to his friends on Facebook: "I'm. Very sorry sguys. It was a pleasure."
Marquez, 24, who wore big, nerdy glasses and dreamed of getting fit enough to join the Navy, has become a focal point of the ever-expanding federal investigation into the mass shooting that killed 14 and injured 21 on Dec. 2. Since the attack, he has checked himself into a mental health facility and agents have searched his house, seized potential evidence and interviewed him repeatedly. Marquez has cooperated, federal authorities said.
On Tuesday, a government official briefed on the matter said federal law enforcement officials believe Farook, and possibly others, considered a terror plot as early as 2011 or 2012, about the time Marquez bought the rifles and converted to Islam.
Farook told at least one associate that he was considering a terror attack, the official said, but declined to identify who that was. FBI agents believe Farook dropped the plan after the arrests of a group of three men in nearby Chino for plotting to kill American targets in Afghanistan, according to the official.
Marquez, who could not be reached for comment for this report, bought the two semiautomatic rifles legally, authorities say. But the weapons were later given to Farook without a recording by a federally licensed firearms dealer, as required under California law.
Marquez, who until recently worked as a Wal-Mart security guard, has not been charged.
Federal agents are also investigating the circumstances of Marquez's November 2014 marriage to Mariya Chernykh, whose sister is married to Syed Raheel Farook, the shooter's older brother. The sisters are from Russia, according to marriage records.
The women came to the United States on J-1 visas, according to a federal official who spoke on condition of anonymity. Such visas are a common way for people who aren't planning to immigrate to visit the U.S. for educational and cultural programs.
Chernykh could not be reached for comment Wednesday, but Marquez's friends and neighbors said there was little evidence he and Chernykh had a typical marriage, or that they even shared an address.
Viviana Ramirez, 23, who met Marquez in an online forum for students at Riverside City College, said he did not live with his wife and never fully explained his domestic situation. On one of the few occasions that Marquez opened up to her about his personal life, Ramirez remembered him confessing that he and his new wife were "not clicking."
Brittani Adams, who lives a few doors down from Farook's brother in Corona, said it looked like Chernykh lived there with her sister and brother-in-law. Marquez visited the house from time to time, but Adams said she never saw him with Chernykh. When she learned on the news that the couple was married, she said, she was shocked.
"He would never leave with her, come with her, not hug her," she said. "The whole thing is very, very weird."
Rosie Aguirre, who lives across the street from the Marquez home on Tomlinson Avenue in Riverside, said she was surprised to learn that Marquez had a wife.
"I've never seen a woman here," she said.
She said Marquez was the one person she saw Farook ever socialize with in the neighborhood. Farook and his family moved to Redlands in May.
Marquez attended prayers at the Islamic Society of Corona-Norco four or five years ago, though not regularly, according to Yousuf Bhaghani, president of the facility's board of directors.
Worshipers may not have remembered Marquez at all, if not for his Latino background, which is unusual at the mosque, Bhaghani said. Those who do remember him said he seemed "like a decent guy who came to pray, nothing that could raise any flags," he said.
Authorities have not contacted the Islamic Society about Marquez, Bhaghani said.
A Wal-Mart spokesman said Wednesday that Marquez had worked for the retail giant since May but that the company had decided to fire him. He did not say why.
Friends have had a hard time reaching Marquez since his name surfaced in connection with the massacre. Immediately after he posted his last Facebook message, one friend wrote back, "You drunk?" There was no apparent reply.
Ramirez said she sent Marquez a message to check on him in the days after the shooting, but he did not respond.
She said her friend had been hoping to join the U.S. Navy. The baby-faced Marquez was an avid bicyclist and had been working on losing weight in preparation for the rigors of boot camp, Ramirez said.
Despite Marquez's links to the terror suspects, Ramirez said she doubts he would have done anything to help Farook and Malik if he knew what they had intended to do with the weapons.
Ramirez is hosting a Christmas party this weekend and said she would still gladly welcome Marquez into her home.
"He's never done anything mean. A lot of newspapers call me and want me to talk bad about him," she said. "He is a really good person."
Times staff writers Richard Winton, James Queally, Rong-Gong Lin II and Zahira Torres contributed to this report.