If Cheryl Grimmer is alive today, an unusual yet recognisable clue remains to her identity. Cheryl, who disappeared from Fairy Meadow Beach almost 40 years ago, had a medical condition that made her bellybutton protrude about 10mm.If she was abducted and raised with another family - one theory that was investigated - she would still be carrying this physical feature or would have had it removed.It is a vital fact about the case that was published only once but never repeated.With the launch of National Missing Persons Week tomorrow, Wollongong detectives are preparing a report for the NSW Coroner on Cheryl's case that may finally put it to rest.Cheryl's brother, Stephen, 45, of Mount St Thomas, said his family was hoping a vital clue would emerge beforehand.Mr Grimmer was just five years old when, on January 12, 1970, he and his elder brother, Ricky, and three-year-old sister Cheryl, went to the dressing-shed at Fairy Meadow Beach.Within minutes the little girl had disappeared, launching one of the nation's biggest manhunts.Despite intensive investigations over the years, not a single clue on her fate has been found.Mr Grimmer said the torment suffered by his family had been immense.He was extra vigilant with the safety of his own children - Jade, 10, and Aiden, 3 - and checked public amenities blocks with almost obsessive compulsion, making sure the buildings were clear of predators."I watch my children like a hawk," he said this week. "Going to the beach, riding a bike - they are never out of my sight."Mr Grimmer said he had little recollection about his sister's disappearance, or the intense investigation and media frenzy that followed."I just remember standing outside the dressing-shed with my older brother, waiting for my sister," he said.The sensation surrounding the case eventually died down, only to resurface over the years when new policing technology emerged.In 2003, police used photographs of Stephen, who is similar in appearance to his blue-eyed, fair-haired sister, to compile a computer image of what she might look like at the age of 37.With the advent of DNA technology, he provided his DNA to the NSW Police database.After 40 years, Mr Grimmer said his sister was always at the back of his mind, especially as his son is now the same age as Cheryl was when she disappeared, and bears a strong resemblance to his dad. "I take the young bloke to the playground at the lagoon there, and look across Puckey's Estate and it makes me think. My mind goes back." REVIEWThe summer Cheryl was stolen: Page 30