Detectives from the Homicide and Major Crime Command are continuing to appeal for witnesses after a plain clothes police officer was stabbed whilst on duty in Bow on 22 November.
A 17-year-old male arrested later that evening on suspicion of attempted murder has been bailed until a date in late January 2017.
Detective Chief Inspector Gary Holmes, who is leading the investigation, said:
"I'd like to hear from any witnesses who saw or heard something that may help us catch the people responsible for attacking this police officer.
"At this stage we have established that the group of four youths had arrived in the area via the DLR, getting off at Bow Church Station. The group was made up of three males and one female. Did you see them leaving the station or in the surrounding area?
"We do not believe that the group were aware that the man they attacked was a police officer, but that one of the males in the group started a verbal row with the officer which culminated in him being stabbed at least three times.
"The officer remains in hospital in a serious condition, recovering from his injuries.
"I would like to appeal directly to the group responsible for the attack and urge them to contact police and hand themselves in."
The investigation has established that the group was also involved in another incident that evening where a motorist was threatened with a knife.
At around 21:00hrs the motorist was sitting in his parked car in Purdy Street near to Devons Road DLR station when the group approached his vehicle and threatened him with a knife. He was not injured.
This incident was initially thought to have occurred after the attack on the officer as it was not called in to police until later in the evening. However, it has now been clarified that it happened around 20 minutes before the stabbing.
Police are also appealing for anyone who witnessed this incident or who saw the group in the vicinity of Devons Road DLR station at around 21:00hrs that evening.
The plain clothes officer, who is attached to a Specialist Crime and Operations Unit, was deployed on a pre-planned operation.
At approximately, 21:22hrs, he was attacked in an alleyway near the Bow Bells Pub, in Bow Road, E3, by a group of four youths resulting in the officer suffering three stab wounds.
After attacking the officer, the group of four ran off.
The London Air Ambulance and London Ambulance Service were called and the officer, aged in his 40s, was taken to an east London hospital where he remains in a non-life threatening condition.
The investigation is being carried by detectives from the Homicide and Major Crime Command.
Anyone with information concerning this incident is asked to call police on 020 8345 1572 or call Crimestoppers anonymously on 0800 555 111.
Enquiries are ongoing.