The transit employee who fatally shot nine co-workers at a rail yard in San Jose, California, had amassed a collection of 12 firearms, multiple Molotov cocktails, and 22,000 rounds of ammunition at his home before setting it on fire, the local sheriff said on Friday. But an FBI official said the blaze that incinerated the house also likely destroyed evidence for determining the precise motive behind Wednesday’s mass murder at the Santa Clara Valley Transportation Authority (VTA) light rail maintenance yard. Authorities say Samuel Cassidy, 57, was armed with three semi-automatic handguns when he opened fire after a morning union meeting at the commuter rail facility in the heart of Silicon Valley, south of San Francisco. Cassidy shot himself minutes later as police arriving on the scene closed in, according to the sheriff’s account. Local NBC affiliate KNTV, citing unnamed law enforcement sources, reported that Cassidy had recently been accused …