SAN DIEGO -- After receiving insider tips and doing weeks of surveillance, the 10News I-Team learned of a security breach in the San Diego public transportation system -- even after I-Team reporter Mitch Blacher discovered millions of Homeland Security tax dollars have been given to the Metropolitan Transit System to improve security.

Less than five miles from the U.S.-Mexico border, off Main Street in Chula Vista, an MTS insider gave the I-Team a tour and showed the security problem.

"Yep, we can walk right in," said the insider.

"So, all these buses are just wide open huh?" asked Blacher.

"Yeah," the insider replied.

Three separate times, the I-Team followed as the insider guided them through an MTS bus yard. For more than two weeks, the I-Team watched as several buses returned from routes only to sit vacant with their doors open and fully exposed.

"You can just walk right on, hide anything you want," said the insider. "There's no problem starting any of these buses. No security, no nothing … this is a hazard because somebody could start this bus right now, back it up and go right out this drive way right here."

"And just drive it wherever they wanted to?" asked Blacher.

"Just drive it wherever they wanted to and nobody would say anything. They'd just drive it right out," the insider said.

During one surveillance shoot, the insider proved that anyone could drive right out of the yard, without even needing a key.

"Can you start the bus?" asked Blacher.

"Yeah, you can start the bus right now if you like," said the insider. "And there it is; the bus is on."

The only person who ever said anything to the I-Team during the yard visit was a man who said he was the maintenance supervisor.

When the I-Team asked where the security office was, the supervisor said, "We don't have a security office."

The I-Team learned this was not the case at every MTS bus yard, as the downtown yard is fully fenced and has a security guard booth.

According to information obtained by the I-Team, federal authorities want the MTS to be secure. The Department of Homeland Security gave MTS $5.2 million in 2009 for "transportation security." Since 2006, the Federal Transit Administration has sent MTS another $1.8 million to be used for safety and security.

The I-Team asked MTS leaders about their security, but spokesman Rob Schupe said they would not do an interview because the issue was a "non-story."

The MTS sent 10News a statement that said, in part, "Passenger safety is MTS' top priority ... trespassing or tampering with buses is a serious crime ... MTS has never had a bus stolen from its properties." MTS also said they have plans to secure their South Bay bus lot by summer 2010.

When the I-Team showed the surveillance video to former Secret Service agent and federal security advisor Glen Winn, he said, "Oh, my … somebody better have a big wake-up call because somebody is going to take advantage of this."

"We contacted MTS and they said, not only do we not want to talk to you, we don't think this is a story," said Blacher.

"I find that appalling, because it is a story," said Winn. "I think the potential for trouble from terrorist-minded people and criminal activity … it is wide open and they've got to fix this immediately."