Officers were called be a member of the public at 1.40pm on Monday to St James Park after the person was found unresponsive.
The man was pronounced dead at the scene.
Detectives are appealing for information and witnesses who may have seen any vehicles near the entrances of the park, or any unusal activity in the park since Saturday evening.
A post-mortem examination on Tuesday found the official cause of death to be a stab wound to the neck.
Formal identification is underway, but police are confident the deceased is 37-year-old Yassar Mustakim Moussa, who lived in Walthamstow.
His next of kin have been informed and are being supported by officers.
DCI Larry Smith, who is leading the investigation, said: “A man’s life has been brutally taken and his body left in a park. We need to know the movements of Yassar from Saturday, 22 August and my team will be working tirelessly to identify those involved.
“This is a busy park with lots of people using it and I’m asking those park visitors, and nearby residents, to really think back over this weekend.
“Did you see anything out of the ordinary? Did you see a vehicle drive in or out of the park through either the north or south gates?
“Someone out there knows what happened to Yassar and I’m asking you to do the decent thing and speak up.
“If you don’t want to talk to us, you can stay anonymous by talking to Crimestoppers.”
Acting North East Borough Commander Waheed Khan said: “My thoughts are with Yassar’s loved ones, who must be devastated not only by his death, but by the callous way in which he was treated.
“I know the local community will be shocked by these events, but please be assured that officers will do everything in their power to find who is responsible.
“Officers will be conducting increased patrols locally so residents can expect to see an additional police presence in the area. We are here for you so please do talk to our officers if you have any concerns.”
This is a breaking story. More to follow…