Details have begun to emerge about the life of the man responsible for killing 12 people in a Colorado movie theater Friday, including the fact that he worked as a counselor at a Jewish-run camp in California.

Jewish Big Brothers Big Sisters of Los Angeles confirmed that Holmes worked at Camp Max Straus near Glendale, California, NBC News reported.

Holmes, then 20, was reportedly in charge of 10 underprivileged kids ages 7-14 at the non-denominational camp when he worked there in 2008.

Holmes himself is not Jewish, and was active in his family’s Presbyterian church, according to the report.

Holmes with an unidentified camper at the camp. (Screenshot: NBC News)

Holmes with an unidentified camper at the camp. (Screenshot: NBC News)

“His role was to insure that these children had a wonderful camp experience by helping them learn confidence, self-esteem and how to work in small teams to effect positive outcome,” the camp said in a statement.

A fellow counselor described the killer to NBC as a loner.

“The entire staff was really close, considering we lived together, except for James,” said the counselor. “He really kept to himself and hardly ever went on any trips with the rest of the staff. He was very shy and reserved.”

On Friday, Holmes opened fire on a midnight showing of the Batman film “The Dark Knight Rises,” in Aurora, Colorado, killing 12 and wounding dozens more. He was captured by police and is being held in solitary confinement without bail.

Holmes had recently withdrawn from a competitive graduate program in neuroscience at the University of Colorado-Denver, where he was one of six students at the school to get National Institutes of Health grant money. He recently took an intense three-part, oral exam that marks the end of the freshman year of the four-year program there, but university officials would not say if he passed, citing privacy concerns.

In a resume posted on Monster.com, Holmes listed himself as an “aspiring scientist” and said he was looking for a job as a laboratory technician.

The resume, first obtained by The Press-Enterprise in Riverside, paints a picture of a brilliant young man brimming with potential: He worked as a summer intern at the Salk Institute for Biological Studies in La Jolla in 2006 and mapped the neurons of Zebra finches and studied the flight muscles of hummingbirds while an undergraduate at the University of California, Riverside.