Is this fake news? The dailymail site has a GPR product that purportedly shows grave sites at the school with high returns. That is unlikely unless the corpses were buried in metal casks a la military graveyards. GPR will not get a return on an organically decomposed body and only a slight return on a wooden cask.
GPR will show disturbed soil. It will indicate that dirt was removed and replaced. The density of the soil and its composition has changed and this will show up.
True story, unfortunately. I saw a documentary about this a few years ago on youtube, with survivors interviewed, and read about this horrific tragic tale.
Considering they have already dug up the cemetery and found human remains, I think we can be pretty certain it’s not “fake”.
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I'm an Archaeological Steward with the Texas Historical Commission, and have worked with GPR in the field.
You have zero idea as to how GPR functions.
The usable data from GPR in a burial context is its ability to discriminate between dense, undisturbed soil, and the looser, less dense, mixed soil in an area that has been dug and re-filled. IOW, it provides a usable image of the backfilled grave, itself.
Try RTFA. It describes GPR results, but not exactly as I have done.