Police want to trace two youths who may have talked to the killer of a nurse.
Cheryl Moss was found stabbed in a nearby park
Cheryl Moss, 33, from Dagenham, east London, was repeatedly stabbed in a park behind St George's Hospital in Hornchurch, Essex, on Thursday.
Officers said the youths may have spoken to a man wearing a dark shoulder-length wig in the park 20 minutes before the attack.
Detectives are still questioning an 18-year-old man who was arrested on Friday in connection with the murder.
He was held after a blue Nike bag was found on the banks of a nearby river.
The bag, which was found by a member of the public on the banks of a river in nearby Upper Rainham Road, is now being tested by forensic experts.
A post-mortem examination confirmed Mrs Moss had died from multiple stab wounds.
Det Chief Insp Dick Langley said: "This was a frenzied attack on a lone woman which took place in daylight hours. Cheryl was attacked in an open space popular with dog walkers, in what appears to be [an attack by a stranger].
"We are appealing for witnesses who may have seen a man carrying a blue Nike bag in the area of Upper Rainham Road [on Thursday] afternoon."
Mrs Moss, who was on a cigarette break when she was attacked, had worked on the hospital's geriatric ward for more than a decade and was described as a popular and respected member of staff.
She was found at about 1100 BST on Thursday and an ambulance was called but she was pronounced dead at the scene. Police said there was no evidence of a sexual attack.
Security has been stepped up at the hospital to reassure staff, who are said to be deeply shocked.
Mrs Moss' family visited the hospital on Friday to lay flowers and read tributes.
Their message, pinned to a floral tribute, read: "Cheryl. Taken so cruelly from us. Will always be in our hearts. Dad and June."