Dozens of criminal investigators combed for evidence at two sites 30 miles apart Thursday to determine if partial human remains found burning in Boston and Bridgewater belong to a single victim.
The grisly discoveries were made about 11 hours apart, first near the Bridgewater state prison complex and later behind a Hyde Park industrial building, where workers smelled a foul burning odor as they arrived at work about 7 a.m. Thursday.
The workers walked to the rear of a one-story building at 20 Readville St., where they saw a smoldering human torso without legs, arms, and head, said one worker, who asked not to be identified.
“Gruesome,’’ the worker said. “It’s unbelievable.’’
A law-enforcement official who had been briefed on the investigation said that the Hyde Park remains were believed to be those of a man, but that forensic work was continuing.
That discovery followed the finding of other partial remains in a burning barrel behind the Bridgewater facility. Authorities would not describe the type or gender of remains found about 8 p.m. Wednesday in the woods off Titicut Street, where Bridgewater firefighters responded to a report of a fire, which had spread from the barrel to surrounding brush.
Firefighters discovered the remains while fighting the blaze and sealed the barrel as evidence, said another law enforcement official with knowledge of the investigation. No trace of an accelerant was found, the official said.
Through the day on Thursday, a stream of investigators from an array of state agencies came and went from the Bridgewater site. About noon, a van belonging to the state’s chief medical examiner left the area.
Titicut Street is an access road to the Department of Correction complex off Route 18, which includes Bridgewater State Hospital, the Old Colony Correctional Center, the Massachusetts Treatment Center for the sexually dangerous, and a substance-abuse treatment facility.
About 2 p.m., state troopers photographed a driveway in the 1600 block of Bedford Street in Bridgewater, about a mile from where the remains were found. Authorities would not say if their work was related to that discovery.
The dual investigations are being overseen by Suffolk District Attorney Daniel F. Conley and Plymouth District Attorney Timothy J. Cruz, whose offices are sharing information.
“We are working together to investigate a potential link between the two scenes,’’ said Jake Wark, a spokesman for Conley.
In Hyde Park, a plumber arrived early Thursday morning to take measurements of a bathroom. Workers from companies that do street repairs and landscaping shared a stunning story: They had found remains of a human body.
The plumber, who identified himself only as Tom, said he and his cousin, who works for the street repair company, decided to examine surveillance video collected by cameras installed on the property only days earlier. They wanted to know if the video might yield clues about the remains.
The surveillance tape showed a person arriving in a vehicle between 3 and 4 a.m. Thursday, tossing something on the ground, and setting it ablaze. “It’s dark, but you can see a car pull in and a shadow come out,’’ Tom said.
After starting the fire, the person drove to the end of the driveway, paused, and signaled before turning left on Readville Street, the plumber said. The type of vehicle and the gender of the driver were not clear from the tape, Tom added.
A law enforcement official confirmed much of the account about the surveillance video, including the assertion that a fire was set about 3:30 a.m.
The torso was found near a large disposal bin in the rear of the building.
Investigators there spent much of the afternoon removing possible evidence in brown paper bags. A short distance up Readville Street, an evidence marker was placed near a faded green Red Sox cap on the sidewalk.
A vehicle from the state medical examiner’s office arrived about 2:30 p.m. and left five minutes later.
One neighborhood resident said she gave police the license number of a suspicious car parked on the street Wednesday night. The woman said she had been walking her dog about 7 p.m. when she saw a man sitting in a large white sport utility vehicle. When her boyfriend walked outside to investigate, the woman said, the man slouched in the seat.
The car, she said, was parked directly beside the spot where the baseball cap had been found.
Mayor Thomas M. Menino’s house on Chesterfield Street sits not far from where the remains were discovered.
The discovery of the remains unsettled residents, some of whom said the area has been plagued by drug problems.
“It’s scary to have something like this going on in your backyard,” said Colby Stephens, who has lived in the neighborhood for six months.
Another neighbor, a middle-aged man who would not provide his name, said the discovery of the remains is the last straw for him. The man, a 10-year resident of Readville Street who was taking his lunch break, said the discovery and the area’s drug problems have convinced him to move as quickly as possible.
“Just another beautiful day on Readville Street,” he said to a postal worker walking up a nearby stoop.
Travis Andersen, John R. Ellement, and Wesley Lowery of the Globe staff contributed to this report. Brian MacQuarrie can be reached at macquarrie @globe.com. Maria Cramer can be reached at email@example.com. Follow her on Twitter @globemcramer. Wesley Lowery can be reached at firstname.lastname@example.org.