We really can't know whether some of the things about this case would end up being legal hearsay, or not, at this point. We just don't have enough information about what LE knows and what evidence they really do have, IMO.
I know there are a lot of people reading here who may be new to these forums, maybe this is even the first case that grabbed your attention. The following comments are really for those individuals. You might be thinking from the general drift of this thread that direct evidence is the strong, "good" evidence and then circumstantial evidence is the tiny, weak little pieces that don't mean much by themselves but can add up. Not so. Circumstantial evidence can also be very powerful, and in fact, potentially can be "better" than direct evidence in the form of an eyewitness to a crime in some situations (eyewitnesses are often unreliable). For example, DNA, fingerprint, and ballistics evidence are all, legally, types of circumstantial evidence. A victim may not remember an attacker's face well enough to identify him but his DNA and fingerprints left behind may do so quite conclusively to a jury.
If you watch a trial that has been televised, you will see this in action. Prosecutors may not have a written or videotaped confession, no eyewitnesses to the crime itself, nor video of the crime taking place, but if they do have some combination of things like DNA, cell phone location records, fingerprints, evidence of purchases of items used in the commission/cover up of the crime, and the opinions of ballistics or tool mark experts (all circumstantial in nature), etc they will have a very strong case.