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Investigators say he was also in the middle of a bitter custody battle with his ex-wife.
The county medical examiner says it appears Mulvaney died of a drug overdose.
Thousand Oaks Mayor Tom Glancy released a statement today.
"A true tragedy unfolded in our community yesterday. We grieve the loss of two young children and devastation of a family," says the mayor.
"We should all take this opportunity to lend support to all of those affected, directly and indirectly, by this act of violence, particularly students from Lang Ranch Elementary School and Los Cerritos Middle School," he added.