MARTINSVILLE, Ind. (AP) — A Labor Day cookout ended in tragedy when a longboat ferrying seven family members capsized on a central Indiana river, killing a 6-year-old boy and a 73-year-old woman, and leaving three men missing, authorities said Tuesday.

It is unclear what caused the flat-bottomed boat to capsize Monday night on the White River near Martinsville, about 30 miles (48 kilometers) south of Indianapolis.

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Two of the boat’s occupants made it to shore, but the boy and woman pulled from the river by emergency responders were later pronounced dead, said Lt. Angela Goldman, a conservation officer with the Indiana Department of Natural Resources.

The search for three men, ages 63, 40 and 32, who were also on the boat was suspended overnight. That search resumed Tuesday morning with authorities using two boats, two airboats, drones and searchers to scour the riverbanks and shallows.

Goldman said life jackets were in the boat, but authorities believe none of the passengers were wearing the floatation devices when the vessel capsized shortly before 9:30 p.m. The family had been celebrating the holiday with a cookout and fishing trip along the river at the DNR’s Three Rivers Public Fishing Area, which includes a large beach and sandbar, she said.

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“It’s just a great big sandbar where you can hang out, grill your hot dogs and fish. They were just enjoying the river together, having a cookout and doing some fishing,” Goldman said.

The boat had already made one uneventful trip across the river to take other members of the party back to the west side of the river where their cars were parked. It was during the second trip that the boat capsized, she said.

Goldman said she doesn’t know why the boat capsized. The river wasn’t flooded and was at a normal late-summer level, she said. DNR officials don’t believe a dam nearby had anything to do with the accident as the vessel was a considerable distance away, Goldman said.

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