The gunman alleged to have killed 12 people in a cinema in Aurora, Colorado, worked as a counselor at a Jewish-run camp in California, just four years ago.
Jewish Big Brothers and Sisters of Los Angeles confirmed that James Holmes, then 20, worked at Camp Max Straus near Glendale, California while studying at the University of California in 2008. He was in charge of 10 underprivileged children, aged between seven and 14.
Holmes is not Jewish and has played an active role in his family's Presbyterian church.
The camp said in a statement: "His role was to ensure 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 outcomes."
Holmes has been declared extremely introverted by fellow councillors and students at his university, having no known friends or social life. One student said: "No one knew him. No-one." He was in the process of dropping out from graduate school at the University of Colorado Denver, although this was for academic reasons, rather than any disciplinary problems.
Officials do not believe that the attack, that also wounded 58, has any terror links. After opening fire, Holmes was captured by police and is currently being held in solitary confinement without bail.