Roger Goodell sent a letter to all NFL employees after the league office was targeted by a gunman in a mass shooting on Monday, July 28.

The deadly violence at a Park Avenue tower is weighing heavy on the minds of office workers in Midtown Manhattan.

Gun laws in the city have largely prevented the sort of mass slaughter common in the rest of America. The last killing of this scale in the city was at a fast-food restaurant in Queens in 2000.

Corporate America is racing to boost security and reassure employees after a shooting left a top Blackstone exec dead, along with four others.

A three-page note found in the wallet of the Park Avenue shooting suspect included several references to CTE, according to a senior official familiar with the investigation. NBC News' Erin McLaughlin explains the possible connections between football,

Former FBI Special Agent Vito Roselli said one of the biggest challenges with safeguarding city buildings is that many lobbies are open to the public.

The New York City shooter who opened fire in a Midtown Manhattan office building has been identified as Shane Tamura. Tamura, of Nevada, shot himself in the chest in the hallway of the 33rd floor of 345 Park Avenue after shooting five people,

A gunman who killed a NYPD officer and three others in a Manhattan high-rise building last night left behind a note that referenced the NFL and CTE, according to sources. MSNBC Investigative Correspondent Marc Santia reports from outside the building.