Camp said investigators think the boy fell through a plastic lid that gave way and into the grease trap embedded in the ground outside the restaurant.
"It's a frightful, tragic accident, misadventure- whatever you call it- just a horrifying situation", Camp said.
There have been similar accidents with grease traps around the country, including one in 2017 that resulted in the death of a 3-year-old Alabama girl.
The child was then taken to the hospital, where he was pronounced dead at noon after "every rescue attempt was made to resuscitate him", Camp said.
"No one ever wants to see anything like this", Camp said, saying it is the "number one" worst thing his officers ever have to deal with.
Camp said that police received a call about a child missing from the location at 10:56 a.m. Minutes later, they received another call that the child had been located.
A spokesperson from Tim Hortons - which is a restaurant chain founded in Canada - told CNN in a statement it offered its condolences to the boy's family.
Restaurant grease traps are created to keep used oil and grease out of sewer systems. In January 2019 Alabama lawmakers passed a measure tightening regulations on traps to make them more secure.
Rochester Police are continuing to investigate the incident.
The city is now pouring concrete around the opening in the ground where the grease trap was located and putting a metal lid on it, according to Camp.
"We have a horrifying episode here that happened today", he said.
The boy has not been identified, but the Times Union reports his mother worked at Tim Hortons and brought him to work with her Monday morning.