Searching for the name of a book about (Possibly) an autistic child...

[Deena]

I read this book years ago, in the 90s or early 2000s (if that) about some sort of murder / case involving a child or person with a disability that I think was the only witness. The person only emitted screeching/screaming noises. Later in the book, they tape the person, and fastforward or rewind or something (the child's speech) and discover that the child is actually just speaking on a different frequency.

Something like that. I've never been able to remember what book this is. It was probably written in the 80s or 90s. I vaguely remember it having a high heel on the cover, but that might be completely wrong.

Can anyone help?