Way, way back at the beginning of this fiasco, Koresh sent ATF the paperwork for several class 3 weapons over a very short period of time. Although not illegal, it raised a huge red flag with the JBT's.
Since Koresh had not done anything illegal, the JBT' couldn't show probable cause for a search warrant. (or any other warrant) In the minds of the govt idiots, no one needs class 3 stuff, especially not a bunch at one time.
So, the govt did a little asking around and found that there had been some child abuse allegations by parents of some of the teenagers living at the compound. The ATF recruited a Texas child protective services investigator,(who doesn't need a warrant) to get inside the compound and have a look around. She found no evidence of child abuse, but she did see a firearm propped against a wall of the gym, and it was as she put it "unsupervised".
Although this gave no probable cause for a warrant, the govt found a compliant judge and lied, variously claiming firearms violations, that a drug lab was inside, kidnapping, etc, etc. Information from one of the clerks in the court indicates that not only did the govt goons get the warrant, they got it with many of the spaces blank to be filled in later.
The ATF was under seige by the beancounters in the GOA, as redundant, and were determined to put on a show that would be used to justify their existence. Koresh was just the right guy, in the right place, at the right time.
BTW, many are wondering why the govt goons shot Koresh from the cattle car when he opened the front door, and prior to trying to serve any warrant. I would remind Freepers of the ROE (Rules of Engagement) at Ruby Ridge. Ie: shoot on sight. While those rules would later be repudiated by the govt, that repudiation had not yet happened by the time of Waco.
The JBT in charge of the Waco shooters was the same murderer who killed Weaver's wife....Lon Horiuchi. Perhaps he was still operating under the assumption that he had the power to kill on sight.