Inside Story - What's Triggering Hate Crimes in the US?

What's triggering hate crimes in the US? The fatal stabbing of two men on a train – and serious injuries to another - has turned the spotlight on bigotry and intolerance in the United States. All three were standing up to a known white supremacist who was heard racially abusing two young women, one of them a Muslim wearing a headscarf. Their alleged attacker is facing trial for aggravated murder and other charges. Was the attack an isolated incident or evidence of a growing trend?