Rest In Paradise Major Harris!! According to his autopsy, investigators believe the 3-year-old was dead for about a week before he was found last Thursday.
Police said a tip led them to North 35th Street and West Rohr Avenue, where Major's body was discovered in a storage container.
Investigators said he was shot in the head and ruled his death a homicide.
Major's mother, Mallery Muenzenberger, 25, of Onalaska, was found dead Oct. 14 in the backyard of a home at North 37th and West Clarke streets.
Major was not found with her.
Investigators believe the mother and son had been in Milwaukee since Oct. 9 when they were killed.
An Amber Alert was not issued for the boy until Oct. 16.
The main suspect in the deaths, Jaheem Clark, 20, of Milwaukee, was found dead from self-inflicted gunshot wounds on Oct. 17.
Police found Muenzenberger's vehicle parked behind a laundromat last Monday.
The SUV had blood inside and WISN 12 learned when someone dropped it off on Oct. 16, they went inside to wash clothes.
The location was one mile from where police found Major's body Thursday.
Police have not said if the person who dropped off the SUV and washed clothes was Clark.
Investigators said Wednesday they arrested six people in connection with Muenzenberger's death.
Four of them were released before Monday.
Police said Monday the other two men, ages 21 and 29, were no longer in custody.
So far, charges have not been filed against any of those arrested.
Police have also not made any additional arrests in the deaths of Major or his mother.
The Medical Examiner's Office also confirmed on Monday that Major's boy had been released to a funeral home in Madison.
Major's father said he intended to bury his son at a cemetery there.
He shared custody of Major with Muenzenberger.
No additional service information was available.
Police have never said why Major and Muenzenberger were in Milwaukee.
Officers said Monday their investigation was ongoing.
They didn't release any other details.