I spoke personally with one of the agents who was shot up. They had several leaks, one of which was when they contracted with a local ambulance company to supply emergency equipment and transport. It happens one of the employees at the ambulance company had a relative that worked on the local paper.
Also, on the day of the raid, a news crew got lost in the area and stopped to ask directions from a postal carrier. During the conversation they happended to mention that the "National Guard" was going to raid the compound, not realizing (or probably not caring either way even if they did know) that the postal employee was a Branch Davidian.
On the morning of the raid, an agent who had infriltated the group was present with Koresh when the postal employee came rushing in and requested an audience with Koresh, telling him what he had learned from the news crew.
Koresh was reported to say that this is it, they're coming. He then shook the undercover agent's hand and wished him well. The agent beat feet out of there and dutifully reported all of this to his superiors, however it was decided to forge ahead when the agent reported that the last thing he had seen was all of the members gathering in the church for prayers. This prayer meeting may have been done for the agent's benefit.
When the team drove into the compound from the main highway to effect the raid, a news team followed them in and subsequently obtained the footage you all saw on the news.