True crime things that haunt you?

This has happened to a relative of mine so this is personal rather than something I’ve read about or seen on the news.
This lady - an aunt of mine had been for a walk on an evening around 7 p.m on her regular route which is frequented by joggers. At around 7:30, my uncle - her husband gets a call from her mobile but from a stranger who told him that his wife was seriously injured and admitted to a nearby hospital. She was found lying on the pavement in a pool of blood with an injury to the back of her head,the nature of the wound making it obvious that she was struck on the head with some metal object. She suffered cerebral haemorrhage and was in a coma. She was on a ventilator for an agonising 2 weeks after which her condition rapidly deteriorated and she passed away. A case was registered and an autopsy done but the trail grew cold. Robbery was not the motive as her wallet and jewellery were intact.
3 years have passed since this incident and we still don’t know who did that to her and why. All we know was that it was not an accident and no one should die such a violent death.
This haunts the entire family even today.