James Markham, 45, was fatally stabbed on the evening of Monday, 9 August after confronting a group of youths in the street.
On Wednesday, a 14-year-old boy was arrested on suspicion of his murder.
A second boy, also 14, was arrested on suspicion of conspiracy to murder.
Both are in custody at an east London police station.
On Thursday, 12 August a 16-year-old girl was arrested on suspicion of assisting an offender. She was taken to an east London police station where she remains at this time.
Police were called to Churchill Terrace at 6.20pm on Monday following reports of a disturbance.
Officers attended with paramedics. They found James who had been stabbed and was seriously injured.
Despite the best efforts of the emergency services and members of the public, he was pronounced dead at the scene.
A post-mortem examination later found he died of a stab wound to the lung.
His next of kin are being supported by specialist officers.
Detective Inspector John Marriott, of the Met’s Specialist Crime Command, said: “We believe that James confronted a group of youths causing a disturbance and was stabbed as a result.
“The brutality of this response is beyond shocking and our thoughts are with James’ family who have been left devastated by their loss.
“The arrests of these individuals is a significant development but we still need the public’s help to build a full picture of exactly what happened on Monday evening.
“I know that there were a number of people present at the time of the murder. I want them to come forward.
“I also believe there will be parents who know that their child was there, or was involved. I am appealing for them to do the sensible thing and get in touch with us.
“A dedicated team of officers is working to piece together the tragic circumstances that led to this murder and to bring those responsible to justice.”
Anyone who witnessed the incident, or has information about what took place, is urged to call police on 101 or tweet @MetCC, giving the reference 5735/09AUG.
Information can also be provided to Crimestoppers, anonymously, by calling 0800 555 111.