Since 15 November, five women have been found dead in the Suffolk town of Ipswich.
Two men, both from the county, have been arrested and are being questioned in connection with the killings.
The Suffolk force has been engaged in its biggest ever criminal investigation, with more than 400 officers brought in to work on the case.
More than 400 police have been drafted in to the inquiry
While the inquiry team is led by Detective Chief Superintendent Stewart Gull, 36 forces from across the country have provided "mutual aid" to assist the Suffolk officers.
These include police divers from neighbouring Norfolk, officers from Northern Ireland and Ministry of Defence police used in various roles.
According to Suffolk Police, officers skilled in producing evidence exhibits and reading documents have all been drafted in.
Vice-chair of the Association of Chief Police Officers (Acpo) homicide working group, Dave Johnston, was also brought in to assess and advise on the progress of the inquiry.
Acpo said the number of officers deployed from forces outside Suffolk, under the control of the Police National Information and Co-ordination Centre, was the largest ever for a murder inquiry.
Suffolk detectives have also been able to call on the large amount of CCTV coverage available to their inquiry.
Police have praised the public's response to the murders
Officers had to analyse images captured in Ipswich, especially the red light area around Portman Road in the centre of the town.
But their inquiries also included CCTV recorded on public transport, leading to the release of footage of one of the victims, Anneli Alderton.
Suffolk Police brought in the Home Office pathologist, Dr Nat Carey, to carry out post-mortem examinations on the bodies of the five women.
He determined the cause of death for Anneli Alderton and Paula Clennell.
Miss Alderton, who was three months pregnant at the time of her death, was asphyxiated.
Miss Clennell, the pathologist determined, was strangled.
However, tests carried out on the bodies of Annette Nicholls, Tania Nicol and Gemma Adams failed to reveal the cause of death.
Officers have carried out many elements of traditional policing.
400+ officers used in inquiry
36 police forces provided staff
7,000+ telephone calls from public
These include extensive door-to-door inquiries, as well as canvassing information from fans attending Ipswich Town matches. The club's Portman Road ground is next to the red light area.
Members of the public have also made more than 7,000 calls to the inquiry team, while the News of the World newspaper offered a £25,000 reward.
Some 10,000 public information leaflets were also printed, providing safety advice for people planning a night out in Ipswich.