A man carrying a high-powered rifle shot and killed four people, including an off-duty police officer working security in Midtown Manhattan, sources told ABC News.

This is a breaking news story. For latest updates, please go to our live blog. An NYPD officer and at least four other victims were killed in a shooting at an office skyscraper in midtown Manhattan Monday evening,

Four people were shot and killed in Midtown Manhattan on Monday. The deceased included two males, one female, and one NYPD officer. One male was also shot and is still in critical condition. The shooter died of an apparent self-inflicted gunshot wound, the mayor said.

Jessica Chen said she and dozens of others barricaded themselves in a conference room on the second floor of 345 Park Ave. after hearing shots fired in the building.

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 44-story building at 345 Park Ave. reopens Monday, one week after four people were killed in a deadly rampage. CBS News New York's Christina Fan reports.

The lobby of 345 Park Avenue will reopen for the first time since last Monday's mass shooting that left four innocent victims dead.