London: A Saudi Arabian student was stabbed 16 times in a “brutal and savage attack” as she walked to university, detectives have said, as police continue to investigate whether the woman was targeted because she was wearing an abaya.

Nahid Al Manea, 31, was walking alone to Essex University when she was knifed to death by a killer who police fear may still be on the loose in Colchester.

Detectives investigating the murder have released from custody a man arrested in connection with the attack.

The 52-year-old man, who was arrested and questioned over the murder on Tuesday night, was “positively eliminated” from the investigation and released late on Thursday, Essex police said.

The development means the killer of Al Manea, 31, is still on the loose.

Al Manea only arrived in Britain in January to begin her University of Essex degree.

Detective Chief Superintendent Steve Worron, of Essex police, said at a press conference, “It is extremely unusual to see an attack of this type. We remain open-minded as to the profile of the offender or offenders.”

Chief Inspector Richard Phillibrown appealed to people in Colchester to remain vigilant until police believed they had enough evidence to remand the killer in custody.

“It’s true we’ve had two knife murders in Colchester in recent months where the motive remains unknown and I would urge anyone to remain vigilant. It’s important that people are aware of their own surroundings, that they don’t go out alone in isolated places, that they take precautions and don’t go out isolated.”

He added: “This murder is an attack on the whole community of Colchester and it’s important we all pull together.”

Detectives have until the early hours of Friday to question the man, who was first arrested on Tuesday night, in connection with Al Manea’s murder.

A post-mortem examination revealed that Al Manea died from 16 stab wounds to her head, neck, body and arms - including two stabs that would have proved fatal on their own.

As police issued a fresh appeal to the public for information. Phillibrown said they were investigating online threats of revenge attacks made in the wake of the murder. “Some of those statements posted on social media are making various threats and the police service is looking at those with the relevant criminal offences in the UK,” he said. “I’d like to assure you that the police will take immediate action against anyone who commits an offence.”

Al Manea had only lived in Britain since the turn of the year, moving to Colchester to live with her brother as she studied an English language course as part of a PhD degree at University of Essex. She was due to graduate in August.

She regularly took the same route to university with her brother along a secluded footpath a short walk from the university’s Colchester campus. However, on Tuesday her brother started lectures early - meaning Al Manea was walking alone when she was ambushed and knifed to death shortly before 11am.