Greater Manchester Police has launched a murder investigation after 15-year-old Kyron Webb died in hospital three days after he was attacked and stabbed.
Paramedics called police to Moston, three miles north-east of the city center, on Tuesday (17 October) shortly after 7.10pm to reports that a boy had been found with stab wounds.
Webb was taken to hospital but died on Friday. An 18-year-old man, a 17-year-old boy and a 16-year-old boy, have been arrested and are being questioned over the attack
A 13-year-old boy was eliminated from the enquiry after being arrested on suspicion of wounding.
It is understood that Kyron was a student at the Manchester Communication College.
Detectives are continuing to appeal for the public's help to work out exactly what happened.
Chief Superintendent Wasim Chaudhry said: "This was a horrific attack on a teenager which has resulted in tragedy.
"My heart goes out to Kyron and his family during this extremely difficult time. I can't imagine what they are going through and we are doing all we can to support them.
"We will not stop until those responsible are brought to justice and I would like to appeal directly to the public to please come forward with any information you have.
"We know the area was busy at the time of the attack and it's likely someone saw something that they don't necessarily realise could prove vital to our investigation.
"If you saw something, please call us. A boy's life has been taken away and his family deserve answers."
Anyone with any information is asked to contact police on 0161 856 9908 or 101 quoting the reference number 1969 of the 17 October 2017, alternatively call Crimestoppers anonymously on 0800 555 111.