Itta Bena, Mississippi (CNN) The KC-130 aircraft that crashed in western Mississippi this week, killing all 16 troops on board, left two "large impact areas," Marines Brig. Gen. Bradley James said Wednesday.

It's not clear how far apart the sites are, but one lies about a half-mile north of US 82 and the other a half-mile south of the highway.

"Indications are something went wrong at cruise altitude," the general said.

Search teams are still finding aircraft parts in the 5-mile debris field, Leflore County Sheriff Ricky Banks said. They found one of the plane's engines Wednesday morning, he said. It wasn't clear if the engine constituted one of the "impact areas."

Also found was a parachute that had not been deployed, Banks said.

Andy Jones, a witness to Monday's crash, said a trail of white smoke followed the plane as it spiraled toward a soybean field. It dropped below the tree line with a bang.

The plane appeared to be upside-down, a Marine Corps official says.

"At first it looked like an acrobatic plane, like a stunt plane, blowing the smoke out the back," Jones said. "Then all of a sudden you realized that the smoke was coming off one of the sides of the wing."

The military is in the recovery phase of the operation, James said. Next, it will work to preserve the impact sites before beginning an investigation, he said. The FBI, the Bureau of Alcohol, Tobacco, Firearms and Explosives and other state and local agencies are assisting in the operation, he said. The National Transportation Safety Board will not participate, as the crash involved a military aircraft, spokesman Peter Knudsen said.

Because the plane was carrying weapons and small-arms ammunition, an ordnance disposal team is working in the area. Anyone removing items from the scene or near it could be criminally prosecuted, state Department of Public Safety Commissioner Marshall Fisher said.

"If the public hears an explosion -- a small explosion, in that regard -- there should be no need for alarm," Fisher said.

On Thursday, Mississippi Gov. Phil Bryant told people to turn over any items found within 5 miles of the crash site. Keeping anything could be a federal crime, he said.

He declared the site an emergency area and ordered flags in the state to fly at half staff on Friday.

Plane headed to California, Arizona

Jones called 911 after he heard the plane hit the ground, describing the final moments before the impact that killed a Navy hospital corpsman and all 15 Marines on board. There were bodies on the opposite side of US 82 from the main crash site, Jones told CNN.

Hercules: Tough, versatile The C-130 family of planes is the longest continuously produced military aircraft. Why it's important: The Hercules can refuel other aircraft midflight. It can fly a small military force and heavy equipment around the world and land on short, unfinished airstrips. It's also used for firefighting, search and rescue missions and the gathering of scientific data from dangerous storms. How many have been made? Lockheed Martin Corp. has produced many variations of the C-130 since 1956. More than 2,500 have been delivered. It has logged 1.5 million flight hours. -- From CNN's Thom Patterson

The crash site, near Itta Bena, is about 100 miles north of Jackson.

CNN aviation analyst Mary Schiavo said that given the two distinct impact points and that the debris is spread out over several miles, it leads her to believe the plane experienced a catastrophic event -- perhaps an engine or propeller breaking off -- that caused the plane to come apart midair.

"That means an in-flight breakup," the former inspector general for the US Department of Transportation said. "That's really rare."

The plane disappeared from Federal Aviation Administration radar at 20,000 feet, about a mile below its flight ceiling, and plummeted uncontrolled to the ground, said a Marine Corps official familiar with the latest preliminary analysis.

Though there is no official conclusion about the cause of the crash and officials continue to review data, video of the aftermath indicates the crew made no attempt to land the plane, and the plane was upside down as it burned in the soybean field, the official said.

This means "there is a high probability" the plane experienced a catastrophe when it disappeared from radar, according to the official. It's unclear if the ammunition on board played any role in the crash, the official said.

It was not clear if the plane was carrying a black box, but Marines spokesman Maj. Andrew Aranda said, "There are some components within the aircraft that record or store information that can be used to aid the investigation."

Two scheduled stops

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Six Marines and a sailor from an elite unit based at Camp Lejeune, North Carolina, were aboard the KC-130T when it went down, the Marine Corps said. The other nine Marines on board were from Orange County, New York, County Executive Steve Neuhaus said. Orange County is home to Stewart Air National Guard Base in Newburgh.

The flight departed from a Marine Corps Air Station in Cherry Point, North Carolina, and was headed to Naval Air Facility El Centro, California.

The plane, which belonged to a Marine refueling and transport squadron, was then scheduled to take the Camp Lejeune-based troops, who belonged to 2nd Marine Raider Battalion, to Marine Corps Air Station Yuma, Arizona, for "routine small unit pre-deployment training," the Marine Corps said.

'He loved the Marine Corps'

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Five victims of the crash have been identified so far.

Staff Sgt. William Joseph Kundrat, 33, was the son of a Marine but "he didn't follow in his dad's footsteps, he marked his own path," his mother, Lynda Kundrat, told CNN.

Her son, a native of Frederick, Maryland, was known to friends and family as "Billy Joe," she said. He married his high school sweetheart and the couple had two children.

"You breathe every breath you take into your lungs because you are American," she said. "And with every breath in their body -- a Marine will fight for you. My son was one of those Marines. He's my hero."

Navy Corpsman Ryan Lohrey, a native of Middletown, Indiana, was identified Wednesday by US Sen. Joe Donnelly of Indiana.

"Ryan served our country with honor and we are grateful for his selfless service. He will be missed, and I send my condolences and prayers to his family and friends," Donnelly said on his webpage.

Gunnery Sgt. Brendan Johnson, a Vermont native, was in the Marine Corps for 23 years.

"He loved the Marine Corps," Brendan's father, Kevin, told CNN. "He loved his job. He liked to fly."

Johnson was a loadmaster on the KC-130, helping manage the cargo on board. In his time in the Marine Corps, Johnson traveled to Europe, Africa, South Asia and the Pacific as well as war zones in Iraq and Afghanistan without any incidents, Kevin Johnson said.

"The old name for it used to be Hercules," Johnson said of the plane carrying his son. "The Hercules C-130s. That's what's surprising; they're a very safe aircraft."

Johnson has yet to receive any answers about the crash.

"They're still calling it an accident. We still don't know what caused it," he said. "We're probably not going to know for a long time."

Dan Baldassare, a Marine from Colts Neck, New Jersey, was also killed, according to a tweet from Monmouth County.

The Freeholders mourn US Marine Dan Baldassare of Colts Neck, killed in the military plane crash. We are forever grateful for his service.🇺🇸 pic.twitter.com/8LCkXXLo4h — Monmouth County (@MonmouthGovNJ) July 12, 2017

"We are forever grateful for his service," the tweet said.

Mark Hopkins of Orange County, New York, was among the dead, a government official said.

"He was a good kid. Young, too young," former neighbor Jim Crawford told CNN affiliate News 12 in Westchester.

Families of the victims have been notified, and a list of victims should be released in coming days, said James, the brigadier general.