DENVER – James Eagen Holmes came from a well-tended San Diego enclave of two-story homes with red-tiled roofs, where neighbors recall him as a clean-cut, studious young man of sparing words.

Tall and dark-haired, he stared clear-eyed at the camera in a 2004 high school yearbook snapshot, wearing a white junior varsity soccer uniform — No. 16. The son of a nurse, Arlene, and a software company manager, Robert, James Holmes was a brilliant science scholar in college.

The biggest mystery surrounding the 24-year-old doctoral student was why he would have pulled on a gas mask and shot dozens of people early Friday in a suburban Denver movie theater, as police allege.