I am not certain they do know more outside of the info from the hundred people they have interviewed which have brought them no viable leads.
What type of evidence would there be? DNA? Not with a burned out shell of a car or on a body burned over 98%, imo. Fingerprints? Not likely. Video evidence? Nope. Liquid accelerant container? Possible, but does not necessarily make a case for homicide. A lighter or matches? No witnesses. No confessions. No leads. She had no fatal wounds (gunshot, stab, blunt force trauma, strangulation, etc) to her body as she died from thermal injury. And they have admitted they have very little and are not moving the case forward. Evidence for homicide? What is left?