SAN BERNARDINO, Calif. -- The investigation of the San Bernardino massacre took FBI divers to a lake near the crime scene on Thursday. They were looking for a hard drive missing from the home of the killers, Syed Farook and his Pakistani wife, Tashfeen Malik.
Another focus is their 24-year-old neighbor.
Law enforcement sources tell CBS News that Enrique Marquez is cooperating with the FBI. He has told them of a 2012 terror plot he and Farook allegedly hatched, then scuttled.
Marquez could face charges of providing material support for terrorism, after admitting he provided the assault weapons used in the attack, which killed 14 people.
But the more that's revealed about Marquez, the more puzzling it is for those who knew him.
"He was really outgoing and he was never violent," Viviana Ramirez, a college classmate, told CBS News. "Just because he was friends with him [Farook] doesn't mean he did it."
Marquez had converted to Islam and visited a mosque a couple of times three or four years ago, according to a spokesman.
A mosque member who met Marquez says he seemed to be searching for direction, was exploring Islam and later said he wanted to convert to Buddhism.
Another friend told CBS News, "When he talked about Islam, he talked about it in the past tense. He told me that he de-converted years ago."
Something else Marquez may have shielded from his friends was that had a wife, a Russian woman who is related to Farook by marriage.
But neighbors of Marquez say they never recall seeing his wife.
Outside the house where family members have shunned reporters for days, Marquez's mother spoke briefly Thursday in Spanish.
"My world is upside down," she said. "My son is a good person."
Marquez lived next door to where Farook once lived.
The first funeral was held Thursday for one of the San Bernardino shooting victims, 27-year-old Yvette Velasco.