PHOTOS: Walnut Creek explosion caused by illegal drug lab

WALNUT CREEK, Calif. (KGO) -- Contra Costa County Fire Captain Kent Kirby says Friday morning's explosion in Walnut Creek has turned into a criminal investigation after police say this was not a gas explosion, but from a drug lab making hash oil - a concentrated form of pot.

Around 10 a.m., fire crews responded to a two-alarm explosion at a six-unit structure at 1564 Sunnyvale Avenue in Walnut Creek, close to the Pleasant Hill BART station.