A New York City police officer and three other people were shot and killed inside a Midtown Manhattan office building on Monday evening by a gunman armed with a high-powered rifle, police confirmed. The suspect, identified as Shane D. Tamura, 27, of Las Vegas, died of a self-inflicted gunshot wound, police said.

While details continue to emerge about a motive for the shooting, CBS News Philadelphia is looking into building security in the city.

The Philadelphia skyline is dense with high-rise buildings and shared office towers. In most cases, securing the skyscrapers is left up to individual property owners and can be costly and time-consuming.

Vito Roselli, a former FBI special agent who spent more than two decades based in Philadelphia, said one of the biggest challenges with safeguarding city buildings is that many lobbies are open to the public. That first point of entry is critical, so having two doors, both requiring a badge entry, gives security personnel a chance to see who's coming.

"You know, another thing that you would want to do is, you want to look, think about giving an advantage to a security guard or somebody inside. So when you come into a glass door, you don't want a security guard, you know, in a direct line of sight," Roselli said.

Some buildings have panic buttons that can stop the elevator and send alerts to employees and police. Investigators said the shooter in New York City was able to access the 33rd floor. Roselli said elevator security is crucial, and "you can do segmentation where you have access cards and you're only able to get to that particular floor with, with that particular access cards."

However, keeping access cards current is important too, such as deactivating former employees or lost cards. Roselli thinks now, after the shooting in New York City, building owners will take a closer look at security nationwide, but it's staying on top of it that matters.

"It takes an obligation from management that they're going to keep funding. They got to keep personnel training. They got to do drills, you know, that's a commitment," he said.

The police officer who was killed in New York City was hired by a private company as a security guard. Philadelphia police have a similar program that allows companies to hire police officers to guard their properties. It's very costly, and most companies use private security firms.