U.S. Capitol Police say an incident early Monday in which a man possessing a gun drove his car through the capitol security perimeter and ran inside before being caught, has prompted a new review of protection measures.

The incident occurred early Monday morning before most members of Congress had returned to resume work in the capitol building where the House of Representatives and Senate are located.

The man drove a sports utility vehicle through a security barrier on the East side of the Capitol, where construction workers have been building a massive underground visitors' center.

After crashing his vehicle into a structure outside, the man jumped out and ran through a construction entrance into the Capitol building itself before police apprehended him in a third floor construction area.

Police identified the man as 20-year-old Carlos Green from Silver Spring, Maryland, and said he carried a small handgun and tested positive for crack cocaine.

No shots were fired, but the incident forced the closure of the Capitol building for one hour, as police stopped visitors from entering.

It wasn't until late Monday that Capitol Police held a news conference to discuss the incident.

Here is acting U.S. Capitol Police Chief Christopher McGaffin:

"We are now conducting the criminal investigation that is ongoing as well as a review of our security measures in the perimeters and access points that we have into the Capitol Visitors' Center as well as the [Capitol] building itself," said Christopher McGaffin.

In the five years since the September 11, 2001 terrorist attacks, the U.S. Capitol has been surrounded by increasingly tight security, including street barriers, police checkpoints, and a ban on large trucks.

Monday's penetration of the security perimeter and the ability of the individual to drive a vehicle almost to the steps of the Capitol prompted questions about how the man was able to get as far as he did.

Acting Capitol Police Chief McGaffin says a review of security procedures will attempt to answer these questions:

"There is a risk when you move a blocked vehicle back, or when you lower a barricade, for another vehicle to intercept," he said. "That is why we have concentric rings of security. Some involve people, police officers who are in posts, some are technology, some are alarm systems, some [are] surveillance, but there are a myriad of security rings that are in place, and in this instance the inner ring of our security initiative was effective in subduing this individual."

The incident at the Capitol on Monday is sure to prompt additional questions from lawmakers at a hearing scheduled later this week to examine progress on the new Capitol Visitors' Center.

At a cost of more than half a billion dollars, the center was designed to help improve security while accommodating the thousands of visitors who come to see the Capitol building each year.