Any defense attorney who has tried enough cases will tell you that sometimes they put in documents requests to the prosecution and occasionally the FBI has to hold a secret meeting with the judge express to the judge that it would hurt national security to release the information.
There are cases where a dependent recognized that top secret technology was being used to catch them and the case was thrown out and the dependent signed documents agreeing to shut their mouth. Some operation trip wire cases were overturned because of this as one example.
Bryan Kohlberger did murder those 4 girls. He also happened to know exactly what technology the police had to investigate his crime.
I think what happened is the FBI used some secret technology, such as satellites taking secret surveillance of the area and knew before the tip came in That it was Kohlberger but had to wait for the correct tip to use in order to cover up the actual technology used.
There is a ton of evidence Kohlberger was being monitored before the security guard called in with the tip, but the tip allowed them to finally connect him to the crime, without having to reveal the classified method of doing so. Remember they were receiving 10000 tops a day, so they just needed the right one to find him, one thay would probably go ignored in regular investigations.
If the defense pushes hard to get ahold of the methods of catching kohlberger, I wouldn't put it past the state to drop charges to protect classified technology used by the FBI