Yorkshire mum was staying in a tent with her boyfriend before she vanished never to be seen again
At the time of her disappearance in August 2003, Lisa Ambler was living 'rough' in a tent in woodland near Halifax town centre.
The mum of two often slept outdoors, with her lifestyle at the time later described by one senior police officer as 'quite chaotic'.
Lisa was 34 years old when she was last seen in Halifax town centre in August 2003 - just over 21 years ago. She had been sharing a tent in woods with her then boyfriend around the time she went missing. The location of their makeshift encampment was given as Southowram Bank, a road which runs through woodland between Shibden Country Park and Halifax train station.
Read more: Baby died after exhausted mum sent home just four hours after birth
Detectives with West Yorkshire Police carried out extensive inquiries to locate Lisa, with senior officers saying that it was possible that she that had come to some harm. The investigation became a murder inquiry when no trace of her could be found.
On the first anniversary of her disappearance, police in Calderdale issued a public appeal for help with the case.
Detective Inspector Dick Nuttall of Calderdale police said: "We are now approaching Lisa's 36th birthday and obviously her family are very anxious to hear any news about where she is."
The detective added: "Nothing has been seen or heard of Lisa since she disappeared.
"It is possible she is alive and well and living out of the area. But police are concerned she may have come to harm, given that inquiries to trace her have been unsuccessful and that her family have received no contact."
In 2012, nine years after Lisa disappeared, there were dramatic developments as police arrested a man, 38, from the Halifax area, on suspicion of murdering Lisa.
The 2012 developments prompted a fresh appeal for information to trace Lisa's whereabouts.
Speaking at the time, Detective Inspector Steve Snow of West Yorkshire Police said: "Extensive enquiries have been made over the years and although eight years have passed since Lisa went missing, we continue to seek the vital pieces of information that could lead us to her.
“It cannot be discounted that after all this time Lisa may well have come to some harm or sadly be dead. However we cannot in anyway confirm this and, in order to bring some closure for her family, we will continue to explore all opportunities which may help us find her."
At the time, Lisa's two children were in their 20s. Her mother had sadly died two years before, not knowing what had happened to her daughter.
Inspector Snow said Lisa's family had not heard from her since she had gone missing. He added: "Lisa lived quite a chaotic lifestyle and was sleeping rough at the time of her disappearance. Her family have not heard from her since the day she went missing and there have been no confirmed sightings."
In June that year police said the arrested man had been released without charge. The Force said the the murder investigation was ongoing and urged anyone with information about her disappearance to come forward.
It was revealed that specialist search teams, including divers, had been involved in in trying to find evidence in June. The searches had focused on railway arches near Berry Lane, Halifax, and the canal basin at Salterhebble, Halifax. It is believed that Lisa often slept rough around the railway arches off Berry Lane.
In 2012, police said their hopes of finding her alive had faded but they hoped a public appeal would provide some answers to her disappearance.
Last year West Yorkshire Police published a list of unsolved murders which were recorded from the year 2000 onwards and which included Lisa Ambler's name and her age at the time she went missing. The brief details were released following a Freedom of Information request. Beneath 'method of killing', the entry for Lisa says 'unknown'.
YorkshireLive has approached West Yorkshire Police for further information.
Get all the latest and breaking news in Yorkshire by signing up to our newsletter here.