The boy _ whose parents, a Toronto couple, have been charged with concealing his death _ died several months ago and was found "near skeletonisation," the report reads.
The document suggests it may prove difficult to determine the exact cause of death due to the body's advanced decomposition, which it describes in detail.
Supt. Steve Brown of the Jamaica Constabulary Force said Monday the report indicates the toddler wasn't murdered.
Police arrested his parents Jan. 15 on discovering the remains and charged them Sunday. They are scheduled to appear in court Tuesday.
The charges come four years after the couple admitted to abandoning their infant daughter in a freezing Toronto stairwell in the dead of winter.
Brown said neighbours in Kingston's inner city area contacted police after they grew suspicious that the boy hadn't been seen for some time.
Officers checked up on the couple but initially found nothing, he said.
Far from reassured, the neighbours "decided to take matters into their own hands" and stormed the home, eventually stumbling across the boy's remains, he said.
"The neighbours were very aggressive," forcing officers to step in and protect the couple, he said.
Local media have reported the parents blamed their son's death on ackee, a native fruit that can be poisonous if eaten raw. But the report indicates ackee poisoning can't be confirmed through tests.
The incident of the infant found abandoned in a freezing stairwell made headlines in Toronto in 2008.
It was -14 C on the January day that Angelica-Leslie _ as she was nicknamed by aid workers _ was found in parking-lot stairwell in east Toronto, touching off a massive police search for her parents.
Police months later arrested the couple in Kitchener, Ont., and charged them with abandoning a child, failing to provide the necessities of life, assault causing bodily harm and criminal negligence causing bodily harm.
Additional charges were later laid against the pair in connection with their three other children, who were all under age six at the time.
Only the father was criminally convicted, but both parents pleaded guilty to a number of offences.
They moved to Jamaica after their children, including Angelica-Leslie, became wards of the Crown.
The couple cannot be identified to protect the identities of the children.
They have consistently denied being the girl's parents, despite DNA evidence to the contrary.
Toronto police said they have been in touch with Jamaican authorities about the case.
--by Paola Loriggio in Toronto