MONCKS CORNER, S.C. » A collision between a small plane and an F-16 fighter jet that killed a father and son was the second fatal tragedy to strike their family in just four days, a relative told The Associated Press.

Michael Johnson and his son, Joseph, died when the Cessna 150 flown by the younger Johnson was torn apart Tuesday in the accident with the jet.

On Saturday, Michael Johnson’s brother and sister-in-law were found dead at their home in Missouri. The couple’s 16-year-old grandson has been charged with second-degree murder in the slayings, police said.

"It’s unbelievable," said Connie Stallworth, the men’s sister. "There just aren’t words to express it. I’m dumbfounded that it happened twice in a few days."

James Johnson and his wife, Beverly, were found dead in their home in a neighborhood of manicured houses with large yards surrounded by farm fields just outside St. Joseph, Missouri.

The couple’s home is at the end of a dead-end road and protected by a steel gate. The front of the large acreage had a "no trespassing" sign as well as a sign with a phone number to call to enter the property.

Kelley Steele, who lived near the two, said the couple and the grandson kept to themselves and did not socialize with neighbors.

"We’re a very close-knit neighborhood, but they just weren’t receptive," Steele said.

Stallworth told The News-Press in St. Joseph that the Johnsons met while working at naval shipyards in South Carolina. She said the couple adopted their grandson after they retired and returned to Missouri. She said Beverly home-schooled her grandson.

In South Carolina, authorities found Michael Johnson’s body in the Cooper River in a sparsely populated area. He was 68. Recovery teams are still searching the same area for his son, who was 30.

On Wednesday, National Transportation Safety Board investigator Dennis Diaz told reporters that his first goal is to document the two crash sites, which are about 10 miles apart. He also said the F-16 pilot, who ejected safely, will be interviewed. But that may not happen for several days.

Investigators will look at flight data recorders and interview witnesses, though that is expected to take months, Diaz said.

He would not comment on the direction, speed or altitude at which either aircraft was traveling.

The jet’s pilot, Maj. Aaron Johnson from the 55th Fighter Squadron, was taken to Joint Base Charleston’s medical clinic for observation, officials from Shaw Air Force Base in Sumter said in a news release.

Maj. Johnson is a 2003 graduate of the Air Force Academy and has been piloting F-16s since 2005. He’s also been an instructor on attack drone aircraft and has been honored with several awards, including the Air Force Commendation Medal and the Aerial Achievement Medal, according to his military personnel records.

The jet crashed into woods around the privately owned Lewisfield Plantation, an estate dating to 1750.

Leo Ramsey, who has worked at the plantation for about 30 years, said he heard the crash and then saw a cloud of smoke.

Ramsey and two other workers found burning metal, splintered trees and a flaming crater where the jet went down, he said.

At the time of the collision, Maj. Johnson was flying solo, practicing instrument approaches to a military base and was communicating with Charleston air traffic controllers, according to Col. Stephen Jost, commander of the 20th Fighter Squadron at Shaw Air Force Base.

Jost said he thought it was overcast at the time of the collision, but he was not aware of any weather-related problems.

It was not clear if a flight plan had been filed, but Berkeley County officials say the civilian pilot had indicated he was traveling to Myrtle Beach.

Warplanes from Shaw Air Force Base, about 35 miles east of Columbia, routinely fly training missions over eastern South Carolina and the Atlantic.

The Cessna 150 is a two-seat propeller plane that typically weighs about 1,500 pounds when fully fueled. By comparison, an F-16 is about 50 feet long and weighs nearly 10 tons, not counting fuel or weapons. The F-16 was not carrying any live munitions at the time of the collision, Jost said.

Jones reported from Columbia. Associated Press Writer Margaret Stafford contributed to this report from St. Joseph, Missouri.