ITTA BENA, MISS.—With debris scattered for miles across the flat countryside of the Mississippi Delta, federal and local officials may be combing soybean fields for up to a week for clues in a military plane crash that killed 15 Marines and a Navy sailor, a sheriff said Wednesday.

Leflore County Sheriff Ricky Banks said the fields are covered with 2 to 3 miles of debris. Reached by phone on Wednesday, he estimated it will take investigators five or six days to sift through the wreckage and clean up the site where the plane crashed on Monday.

Meanwhile, Mississippi Gov. Phil Bryant warned people not to remove debris from the area and said that anyone taking something could be prosecuted.

Bryant, in statements Tuesday on Twitter, said law enforcement authorities have received reports that items are being taken from the crash site. Debris from the KC-130 is scattered for miles.

Read more: At least 16 die in military plane crash in rural Mississippi

Sheriff’s deputies and state troopers have been trying to control access to sites, but the broad area and number of roads makes that difficult. Bryant asked people to stay away and turn debris over to authorities.

Six of the Marines and the sailor were from an elite Marine Raider battalion at Camp Lejeune, North Carolina, and were headed for pre-deployment training in Yuma, Arizona, the Marine Corps said Tuesday.

Several bouquets were left at the main gate of Stewart Air National Guard Base in Newburgh, New York, where the plane was based. Officials said some of those killed were from the base, but Stewart was closed to reporters and did not issue a statement.

“We’re feeling the pain that everybody else is,” Robert Brush said after dropping off three pots of red, white and blue petunias. He works for a landscaping company that serves the base.

Military officials continued to withhold the names of the dead, saying they were notifying family members.

Witnesses said they heard low, rumbling explosions when the plane was still high in the sky Monday, saw the aircraft spiralling toward the flat, green landscape and spotted an apparently empty parachute floating toward the earth. It was the deadliest Marine Corps air disaster since 2005, when a transport helicopter went down during a sandstorm in Iraq, killing 30 Marines and a sailor.

The crash happened outside the small town of Itta Bena about 135 kilometres north of the state capital of Jackson. Bodies were found more than a mile from the plane.

The Marine Corps said the cause was under investigation and offered no information on whether the plane issued a distress call.

FBI agents joined military investigators, though Marine Maj. Andrew Aranda told reporters no foul play was suspected.

“They are looking at the debris and will be collecting information off of that to figure out what happened,” Aranda said. The county coroner, meanwhile, ferried more body bags into fields to remove remains.

The KC-130 is used to refuel aircraft in flight and transport cargo and troops.

Will Nobile, a catfish farmer, was inside his office Monday afternoon when he heard an unusually loud rumble in the sky.

“It sounded like a big thunderstorm,” Nobile said. “Not one big explosion, but a couple of second-long explosions. . . . A long, steady rumble is what it was.”

He walked outside to see what was making the noise in the cloudless afternoon and saw a “grey streak” disappear behind trees, and then black smoke rising.

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Andy Jones said he was working on his family’s catfish farm just before 4 p.m. when he heard a boom and looked up to see the plane spiralling downward with one engine smoking.

“You looked up and you saw the plane twirling around,” he said. “It was spinning down.”

Jones said that by the time he and others reached the crash site, fires were burning too intensely to approach the wreckage. The force of the crash nearly flattened the plane, Jones said.

Nobile said he drove to the site and as he and others stood by a highway, they saw an open parachute wafting down from the sky: “It didn’t look like anybody was in it.” Another catfish farmer found an empty, open parachute later near a fish pond, Nobile said.

Jones said firefighters tried to put out the blaze but were forced back by an explosion. The Marines said the plane was carrying personal weapons and small-arms ammunition — equipment that may have contributed to the explosion and the popping that could be heard as the wreckage burned.