"Preliminary results indicate Mr Cottrell's injuries were consistent with blunt impact trauma and multiple fractures to his head, neck and extremities (left arm), including extensive brain injuries."
Mr Miller said a courier driver who had been in the area at the time had been found but police were still seeking a male and a female walking in the area, as well as a taxi driver.
"We do not believe any of these people are connected in any way either but would like to speak to them to ascertain if they saw or heard anything suspicious," Mr Miller said in a statement.
A large amount of CCTV footage had been obtained and staff had begun to analyse it, a process that would take some time.
"I remain confident that we will locate those persons responsible for this vicious and cowardly attack and bring them to justice," Mr Miller said.
