Police investigating the murders of a Saudi student and a vulnerable man in Essex say they have recovered 38 knives during their search.
The update on the investigation came as Crimestoppers announced a reward of £10,000 for information leading to the arrest and conviction of Nahid Almanea's killer.
The 31-year-old was stabbed 16 times as she walked along the Salary Brook Trail footpath in Colchester on June 17.
Police are looking into a possible link between Ms Almanea's murder and that of Jim Attfield, who was stabbed 102 times on his arms, hands, back, neck and head in what police described as a "frenzied" attack two months earlier.
Police look for clues in the hunt for Ms Almanea's killer A £5,000 reward that was previously offered for information about his death has been doubled to £10,000.
Detective Chief Superintendent Steve Worron, of Essex Police, said the 38 knives recovered so far were being examined to see whether any of them were used in either attack.
Hundreds of officers from several different forces have spoken to more than 100 witnesses and carried out door-to-door inquiries at 325 houses, he added.
On Tuesday, police said they were trying to trace a man who may have followed Ms Almanea four days before she was killed.
Ms Almanea was seen on CCTV the day before she was attacked Witnesses said the man walked behind two women as they came out of a house in Stanley Wooster Way at around 8.45am on June 13.
He is described as white, in his 30s, around 5ft 10in tall and with short, dark hair. He was dressed casually and was wearing dark jeans.
Police have said they do not have evidence that the murders of Ms Almanea and Mr Attfield are linked or that a serial killer is involved.
However, "parallel" investigations are being carried out and they have admitted there are obvious similarities.
Witnesses are asked to contact the incident room at Essex Police on 01245 282103. Alternatively, call Crimestoppers anonymously on 0800 55111.
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Shehnila Taufiq and her three children died in the attack
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Police want to speak to witnesses who potentially saw the offender