U.S. police on high alert in response to threats

NEW YORK -- Police officers across the country are on high alert this week, in response to ongoing threats against police. The fatal shootings of two NYPD officers has spawned numerous threats of copycat assassinations. In New York alone, police have investigated at least 80 threats.

The FBI warns that police are being targeted and threatened after nationwide anger following the deaths of unarmed black men in New York and Ferguson, Missouri.

NYPD police commissioner Bill Bratton said, "There's been an excessive 80 of those over the last week or so. We've closed out quite a few of them. We've made upwards of 15 arrests related to those events. Any threat made against my officers is going to be dealt with very quickly, very effectively."

One concern is copycats in the wake of the assassination of two police officers in New York City.

According to a new report, of the 50 officers killed last year, 15 were killed in ambush assaults in 2014 and police shooting deaths were up 56 percent over last year. That is according to the National Law Enforcement Officers Memorial Fund.

In Houston, officials have now assigned two-officer units for the first time after random shots were fired at police. And from Los Angeles to Tampa to Philadelphia, police have found themselves under attack.

In St. Louis, several protesters were arrested after storming police headquarters.