Also from that link above, Becky's mother Karen Edwards believes Halliwell killed several more girls:
‘He is definitely a serial killer,’ says Karen, 55, with absolute conviction. ‘I believe he has been up and down the country murdering young women. He used to be a groundworker up north – I know somebody who worked with him on the same building site. He would go and have a pint with the lads and then disappear. Serial killers are usually triggered by dates. That [19th March] was the day that Halliwell broke up with one of his partners.
Claudia Lawrence - 18th/19th March 2009
Halliwell was familiar with York – his father lived in Huddersfield – and the description of Claudia’s murderer is identical to him – a left-handed smoker, 5ft 8-10in, with slightly receding hair and a skinny build. ‘Claudia was reported missing from her home on March 19, 2009 – exactly two years to the day before Sian. It is also the same date that Linda Razzell disappeared.’
http://www.websleuths.com/forums/showthread.php?286731-UK-Claudia-Lawrence-35-York-University-18-March-2009-Chef-2/page8
Linda Razzell - 19th March 2002
Karen is convinced that Halliwell is also responsible for the murder of Linda Razzell, who disappeared on March 19, 2002, after dropping her children off at school and driving into Swindon town centre. Her husband Glyn was convicted of her murder but always protested his innocence.
http://www.websleuths.com/forums/showthread.php?17872-UK-Linda-Razzell-Davies-Wiltshire-19-March-2002-*G-Razzell-guilty*&highlight=razzell
Sally Ann John - 8th Sept 1995
Karen believes Halliwell may have killed 23-year-old prostitute Sally Ann John, who was classified as a missing person in 1995.
‘She was a Swindon girl and knew him well,’ she says. ‘She used to live in the same street as Halliwell, baby-sit his kids and take his taxis.’
No thread
Melanie Hall - 9h June 1996
She also thinks that he was involved in the murder of Melanie Hall, who disappeared from a Bath nightclub the following year. ‘She was taken by an unmarked taxi,’ adds Karen. ‘He has to be in the frame.’
http://www.websleuths.com/forums/showthread.php?131706-UK-Melanie-Hall-25-Bath-Somerset-9-June-1996&highlight=melanie+hall