Timeline: Sian O'Callaghan murder
Office worker Sian O'Callaghan, from Swindon, was last seen alive leaving a nightclub in the Wiltshire town.
Five days later, police investigating her disappearance confirmed her body had been found and an extensive search was under way for a second possible murder victim.
The following shows the key events in the search for the 22-year-old and the investigation into her death.
19 March 2011
Sian O'Callaghan is last seen leaving the Suju nightclub in Swindon alone at 0252 GMT to walk half a mile home to the flat she shares with boyfriend Kevin Reape, 25.
At 0324 GMT Mr Reape sends a text message to her mobile phone. Cell site analysis later reveals her phone was in the Savernake Forest area, near Marlborough.
At 0945 GMT Mr Reape contacts police and reports Miss O'Callaghan missing.
20 March 2011
Police issue an appeal for information and reveal they have been searching the 4,500-acre Savernake Forest.
21 March 2011
Det Supt Steve Fulcher, who is leading the investigation, says it has been established that Miss O'Callaghan's LG E900 Optimus mobile phone had activated in a six-and-a-half mile radius of the mast at Cadley.
At 1500 GMT Mr Reape appeals for information to help find her at a news conference.
Also present are Miss O'Callaghan's parents Mick, 51, and Elaine, 48, and younger sister Lora, 19.
Detectives release CCTV of Miss O'Callaghan leaving the Suju club.
22 March 2011
About 400 people, including Miss O'Callaghan's friends and Mr Reape, help search Savernake Forest after police appeal for the public's help.
An anonymous donor offers a £20,000 reward for information to help find her.
23 March 2011
Police say further use of mobile phone technology had produced several "hot spots" that specialist search teams are examining.
The public are asked not to join the searches.
Det Supt Fulcher says the inquiry is moving at a "rapid pace" with "significant lines of inquiry being developed".
About 200 people attend a vigil for Miss O'Callaghan.
24 March 2011
Specialist dog teams are brought in to aid the search through woodland.
Police make an "urgent" appeal to anyone who saw a green Toyota Avensis estate taxi on the day Miss O'Callaghan disappeared to contact them.
The reward to help find her rises to £40,000.
A man is arrested on suspicion of kidnap at a supermarket in north Swindon where police also seize a green Toyota car.
A police tent is erected in the front garden of a house on Ashbury Avenue in Swindon.
Police confirm a number of locations are also being searched as part of the inquiry.
Police find Miss O'Callaghan's body and search for a second possible victim after arresting a 47-year-old man on suspicion of double murder and kidnap.
25 March 2011
Police investigating Miss O'Callaghan's murder say they are searching for the body of another person who went missing from Wiltshire "several years ago" at Eastleach in Gloucestershire.
26 March 2011
Police are granted until the early hours of Monday to question the man being held in connection with Miss O'Callaghan's murder.
Police searching for a second body near Eastleach in Gloucestershire find human remains.
At 2120 GMT, Christopher Halliwell, 47, of Ashbury Avenue, Swindon, is charged with the murder of Miss O'Callaghan.
28 March 2011
Mr Halliwell is remanded in custody by Swindon magistrates to appear before Bristol Crown Court on 30 March.
Miss O'Callaghan's father Mick says the family's pain at hearing of her death is "raw and overwhelming".
30 March 2011
Mr Halliwell is remanded in custody to appear via video link at Bristol Crown Court on 8 April. No application for bail is made.
1 April 2011
An inquest into Miss O'Callaghan's death is opened and adjourned at Oxford Coroner's Court. The hearing is told she is likely to have died of head injuries.
Hundreds of people march through Swindon in memory of Miss O'Callaghan.
4 April 2011
Police say they have identified a woman whose remains were found near Eastleach in Gloucestershire.
5 April 2011
Police name the woman whose remains were found near Eastleach as Becky Godden, from Swindon, who had been missing for eight years.
6 April 2011
Karen Edwards, Becky Godden's mother, is joined by about 20 friends and family to lay flowers and a teddy bear at the site where Miss Godden's body was discovered.
8 April 2011
Mr Halliwell appears via video link at Bristol Crown Court from Long Lartin prison.
The case is adjourned until 14 July for a plea and case management hearing.
18 April 2011
Hundreds of people line the streets of Swindon for Sian O'Callaghan's funeral.
31 May 2012
Halliwell denies murdering Sian O'Callaghan at Preston Crown Court but a charge of murdering Becky Godden is removed from the indictment. Mrs Justice Cox rules that evidence gained following his arrest was inadmissable.
19 October 2012
Halliwell pleads guilty at Bristol Crown Court to murdering Sian O'Callaghan. He is sentenced to life imprisonment and must serve a minumum of 25 years.