James Markham, 45, was stabbed to death after confronting a group of young people on the street on Monday.
On Wednesday, a 14-year-old boy was arrested on suspicion of murder, and another 14-year-old boy was arrested on suspicion of conspiracy to murder.
The couple are still detained at a police station in east London.
At 6:20 pm, the police were called to Churchill Terrace in northeast London.
The public, together with police officers and paramedics, tried desperately to save Mr. Markham, but he died on the spot.
An autopsy confirmed that he died from a lung stab wound, and his close relatives are receiving support from expert officials.
DI John Marriott of the Metropolitan Crime Professional Command said: “The cruelty of this response is shocking. We are with James’ family and they are deeply grieved by the loss.
“The arrest of these two people is a major development, but we still need the help of the public to fully understand what happened on Monday night.
“I know a lot of people were there when the murder happened. I want them to come forward.
“I also believe that there will be parents who know that their children are there or are involved. I call on them to do wise things and get in touch with us.”
The officials continued their efforts to piece together the details of the murder.
