A lawyer for the teacher said that on the day of the shooting, concerned teachers and employees warned administrators three times that the boy had a gun on him and was threatening other students.

Scant paper trails, as well as accounts from a few neighbors and friends offer a fragmented portrait of a lonely, embittered man for whom dancing may have offered a rare reprieve from an otherwise empty life.

California is still reeling from an earlier attack on a Lunar New Year celebration in Monterey Park that killed 11 and cast a shadow over an important holiday for many Asian-American communities.

The death toll rose to 11 on Monday after one of the 10 who were wounded died.