A New York City office building where a gunman killed four people then himself has reopened a week after the deadly shootings. On Monday, workers trickled back into 345 Park Avenue in Midtown Manhattan, a skyscraper home to high-profile tenants including the NFL and asset management firm Blackstone.

Blackstone said its headquarters at 345 Park Ave., will reopen Monday, but employees have the option to work remotely. Windows of the building that were shattered by bullets last week have now been replaced.

The lobby of 345 Park Avenue reopened for the first time since last Monday's mass shooting that left four innocent victims dead.Monday marks one week since the tragedy and it isn't an easy day for employees who returned to work.