The Palmetto State Armory M4 assault rifle used in the shooting that killed an NYPD cop and three civilians is .223-caliber and is equipped with a black scope, a handguard, and a shoulder sling. The AR-style gun retails for around $500 and was equipped with a high-capacity magazine.

Police are investigating a reported active shooter at a Midtown Manhattan high-rise. Here’s what we know about the suspect involved in the incident near Park Avenue.

The 27-year-old Nevada man left a note at the scene voicing anger that his mental illness may be linked to his having played football, officials familiar with the investigation told NBC News.