THE detective leading the Sian O'Callaghan murder investigation has thanked the public for their help and support.

Speaking at a press conference minutes ago, Detective Superintendent Steve Fulcher said the help had been invaluable.

"The inquiry team were all desperately hoping for a positive outcome," he said.

"Early on Saturday morning Sian was reported missing by her boyfriend Kevin.

"Sian was a lovely girl from good family. Her not contacting friends and family at that time was out of character."

He also described her as being "very sociable".

"Having examined the case and being concerned I did certain things.

"As a result of CCTV available from Suju, her intention, we believe, was to go home and nobody has seen or heard from her since.

"We know her mobile phone was live at 1.15am as texted Kevin. At 3.24am Kevin got that having been asleep and texted her back - 'Worried x'."

He reiterated information that her phone was somewhere in the Savernake Forest area at 3.24am and police had a six-and-a-half mile area to search.

"We had a breakthrough on Tuesday as further CCTV footage gave an indication that the abduction of Sian was committed by an individual driving a green Toyota Avensis," he asid, Further analysis of the footage allowed them to identify registration.

"Our primary objective was finding Sian, hopefully alive and well. All of the things we've been doing the last few days are vitally important."

The 47-year-old man in custody, named as Christopher Halliwell, is still being questioned by police.