Hamilton police say they believe the death of an 11-year-old boy with disabilities who was the subject of an Amber Alert over the weekend was an accident.

The body of Finnigan Danne, who suffered from a neuromuscular disorder and had limited mobility, was found Sunday afternoon in a culvert not far from his home in the west Hamilton community of Dundas.

An autopsy was conducted Monday and the cause of the boy's death was determined to be drowning.

Police said officers and neighbourhood volunteers had searched the area where the culvert -- a storm sewer under the roadway -- was located but had not initially spotted the body because it was submerged in the water.

The body of the boy, who was initially reported to be 12 years old, was found during a later police search.

Danne went missing from his home Saturday morning, and police reported that he had been found dead Sunday evening.

Jon Bailey, who lives three doors away from Danne and spent most of the weekend looking for the boy, said he had partially crept through the culvert himself earlier in the search.

"It's a horrible feeling...I just wish I'd searched a bit harder," he said.

"I had walked in and I had gotten about 10 feet in and I slipped, and my shoes had gotten soaked, my flashlight shorted out. Instead of keeping going, I just turned around and walked out...I just kind of dismissed that spot, thinking that maybe somebody else had gone there, maybe police were going to go there. I wish I hadn't."

Moira Leggate, who also helped search for Danne, was just as shocked at where the boy was found.

"I'm stunned, because it was a really extensive search. The police were here on horseback yesterday, they went down there, I saw them do it," she told reporters after Danne's body was found. "The police were here with the dogs from yesterday from about two o'clock. I was with them. We didn't leave anything unturned."

Bailey said he had been away from home when he saw a Facebook post about Danne's disappearance. When he returned to the community, Bailey said police officers and paramedics were outside Danne's home, while some area residents were on the street.

Two women, one of whom helped care for Danne, told him the boy had gone searching for his cat after the feline escaped earlier Saturday morning, Bailey said.

Danne was thought to have left his home without his wheelchair, Bailey said.

Police had set up a post outside Danne's house and advised volunteers to start looking for the boy under bushes and in crevices in the area.

"I just grabbed my running shoes and headed out," said Bailey, who searched the surrounding area for seven hours on Saturday, and again on Sunday until word spread that the child had been found.

Initially, however, the community didn't know if the boy had been found safe.

"It was just a bizarre experience, no one knew what was going on," said Bailey. "There was people lined up all down the street."

Staff Sgt. Marty Schulenberg said a police officer had to physically go into the culvert to confirm that they had found Finnigan, more than 24 hours after he went missing.

"The visibility is very poor, even with flashlights. The visibility is very limited. Even when Finnigan was located, it was difficult to determine, at first, whether or not we had located his body," he said.

Hamilton police Det. Dave Brady said investigators initially believed they would be able to find Finnigan near his home, and they decided to issue an Amber Alert after the search turned up nothing. Amber Alerts are typically used in suspected cases of child abduction.

"The investigation is fluid, it is reconsidered at all time and we consider all possibilities," Brady said.

Det. Brady said the boy wandered away from his house without his mother's knowledge. He said there was a previous incident where Finnigan had gone missing, and was later found hiding.

"How he ended up in the culvert, it would seem that he probably crawled in there as a young boy who likes to hide," Brady said.

Police do not suspect any foul play in the boy's death, and call it a "tragedy."

A candlelight vigil for Danne is planned in the community for Tuesday evening.