Homeless and hopeless: How did an ordinary life end so brutally?

Amid the crumbling factories, disused industrial units and debris of a small community blighted by drugs, detectives are stepping up the search this weekend for a vital clue that could solve one of Scotland's grisliest murders.

The dismembered body of 19-year-old Amy Anderson was discovered on the shores of the river Leven at Alexandria, West Dunbartonshire, near Glasgow last month. Scotland has been shocked by the speed with which a girl from a respectable, loving family descended into the nightmare of drugs, deprivation and a horrific death.

Detectives hunting the killer are still trying to trace Amy's final movements. They say that in a period of only 13 months she had been transformed from a "lovely, good- natured girl" with "spirit and promise" into a heroin addict, petty criminal and prostitute.

Despite an unsuccessful appeal on BBC's Crimewatch this week, Strathclyde officers are pursuing several leads. Detectives say they have been able to pinpoint the time of death to within 36 hours and widened their search for the drivers of a blue Transit or Sherpa van and a light-coloured Ford Escort van that were seen either on the towpath or the area near the river Leven between late evening on Tuesday, 7 May and lunchtime on Wednesday, 8 May.

Amy had possibly been killed in another part of the area and her body parts taken to the river in bags.

There is no evidence that the teenage mother was involved in drug dealing. The police know she had been funding her habit by petty shoplifting and selling sexual favours on the streets of Alexandria for as little as £9, the price of a bag of heroin.

Her final months as a pregnant, homeless junkie, sleeping rough with her 26-year-old boyfriend, were a world away from the middle-class life into which she was born. Amy was brought up in the picture-postcard village of Crossmichael, Kirkcudbrightshire, by her parents, Ian and June. She had two elder sisters, Greer and Gayle. When her parents separated, Amy moved to Dumfries with her mother and appeared to settle down and do well at school.

But it was there that her downward spiral began after she met her boyfriend, Brian Galloway, who had moved to Dumfries from Alexandria in an attempt to give up drugs. Within months the besotted teenager became pregnant and gave up her place at catering college to move with Mr Galloway to Dunbartonshire, where the couple had a daughter, Lauren, now aged one.

However, Amy rapidly became hooked on heroin. She was evicted from her flat in Alexandria and after the intervention of social services six months ago, her baby was placed in Mrs Anderson's care. Amy spent her last days living in an abandoned industrial container with a makeshift bed and a candle for light.

More than 90 police officers are involved in the murder inquiry. Detective Super-intendent Stephen Ward, who is leading the investigation, says they will pursue every possible lead.

"The person responsible for cutting up the body would have been covered in blood, they must have been acting extremely strangely," he said. "I would appeal for anybody with any information to come forward."