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

On Monday evening, a man armed with an assault rifle walked into 345 Park Ave. and killed four people before fatally shooting himself.

"Is this safe? Is it OK?"

Many office workers received emails Tuesday offering reassurance their safety was a top priority.

Some included links to review active shooter protocols, such as using furniture as barricades as seen in photos taken inside 345 Park Ave. during Monday's attack.  

"There's a general thought process of – is this safe? Is it OK? But you know, we gotta work, so we're here. That's pretty much it," office worker Jason McPherson said.

"They've already sent a notification to all of us telling us that they will be addressing higher security for not just us, but all of the buildings they have tenants in," office worker Christine Torres said.

Shooting will prompt look at new security tech, expert says

One of the shocking images from Monday's violence shows the gunman strolling into the building with a rifle by his side.

Spotting an approaching threat on security camera is no guarantee of stopping it, according to retired FBI Agent Kenneth Gray, now on the faculty at the University of New Haven.

"You still have response time. Police still have to get from wherever they are to wherever the bad guy is, and so if it only takes him 20 seconds to walk from his car into the lobby, that's probably faster than what police can respond in," he said.

Security expert Don Aviv said the shooting will prompt a look at new security technologies and protocols.

"No one technology will save the day. It's the entirety of a program. You have to look at everything from soup to nuts. What are the threats against the organization? What technology would best mitigate those threats?" he said.

Mayor Eric Adams told "CBS Mornings" that 345 Park Ave. has bathrooms that double as safe rooms with lockable, bullet-resistant doors.

Aviv said 345 Park Ave. had more robust security than many Midtown buildings, pointing to the difficulty of stopping a determined attacker.