BOULDER, Colo. -- The intrusion into Boulder High School by two men in camouflage is raising questions once again about school security.

The school has several entrances, but they're generally locked all day long. The main entrances are unlocked at 6:30 a.m. for students and staff.

Police said the kitchen manager spotted the intruders in the cafeteria at 6 a.m. and yelled at them to get out.

Investigators spent a good part of the day trying to figure out how the intruders got into the school.

"There is no sign of a break-in," said Boulder Police Chief Mark Beckner.

Deputy Superintendent Chris King said, "There are several tunnels under the school (for utility and sewer lines) but to my knowledge no one has gained access through them."

The school is monitored by 15 exterior cameras, but none inside. There used to be one in the cafeteria and one in the courtyard, but district officials said they were removed in 2001 because several members of the community felt they were too intrusive.

The exterior cameras are operational, according to Chief Beckner. "About one hour prior to the incident, two people were seen running eastbound from the school."

The chief said he doesn't know if there is a connection between the people seen running on the videotape and the actual intrusion.

He also said cameras inside the school may not have made a difference. "We have cameras in banks and we still have bank robberies."

The deputy superintendent agrees. "There are some schools of thought," King said, "that the more you make a school too tight and prison-like that that can actually compromise safety because it creates an 'us versus them' environment with students and adults."

In addition to the exterior cameras, King said Boulder High has three campus monitors (security agents), two SRO's (school resource officers) five administrators, 100 teachers and an alarm system to help keep students safe.

He said the alarm system includes motion detectors.

Police said the alarm system was not triggered during the night, which leads them to wonder if the intruders followed an employee into the building.