"YOU know who you are and what you have done. Search your conscience. Hand yourself in.”

Det Chief Supt Steve Worron has appealed directly to those responsible for the deaths of James Attfield and Nahid Al- Manea to hand themselves in.

Nahid, 31, was living with her brother in Woodrow Way, Colchester, and studying English language at Essex University.

She was stabbed 16 times and killed on the Salary Brook Trail shortly before 10.40am on Tuesday, June 17.

James “Jim” Attfield, 33, of East Bay, Colchester, was stabbed 102 times and found near Castle Park just before 6am on Saturday, March 29.

Mr Worron said: “You have committed a truly dreadful action. It has devastated a family and communities across the world.”

Speaking about Mr Attfield, he added: “James was a young man tragically injured in a road traffic collisionwho was working hard to rebuild his life when he was brutally murdered. You know who you are and what you have done.

"Search your conscience. We will deal with you sensitively, professionaly and with respect, but hand yourself in.”

Mr Worron urged people to remain vigilant while the killer or killers are on the loose and said officers are as determined as anyone to find the perpetrators and get justice.

He said: “It is extremely unusual to have two knife related acts of such ferocity in quick succession.

“We have no witness who has seen the killer or killers. But we are committed to making sure we get justice for James and Nahid, their families and the wider community of Colchester.”

Anyone with information can call the incident room on 01245 282103 or Crimestoppers on 0800 555111, and many people have.

Dozens have come forward with information about the man seen running from the scene in a red top following the release of an e-fit with police continuing their enquiries.

Since the investigation began officers have taken more than 200 statements from the public, received 527 calls into the incident room and visited more than 600 properties.

Det Chief Supt Steve Worron said: “The investigations currently running are two of the largest run by Essex Police in the last ten years. Our message to family and friends of Nahid and James is we have an absolute commitment to doing everything we can to bring the person or people responsible for their killings to justice.

“There are still a significant number of forensic lines of inquiry, but I can’t say with certainty anything we have recovered identifies their killers.”

More than 2,100 exhibits are being analysed.

However the knife found in Hawthorn Avenue has been ruled out of having any connection with the murders which have received international attention.

Almost one million people watched the video of one of the first press conferences following the murder of Nahid Al-Manea.

In three days there were 970,000 hits on YouTube including 350,000 from Saudi Arabia.