KABUL, Afghanistan (AP) — International military forces worked today to recover every last piece of a Chinook helicopter that crashed over the weekend, killing 30 American troops, seven Afghan soldiers and an Afghan interpreter, NATO said.

Among the fallen reportedly were Dave Carter, a 1982 graduate of Hays High School, and Bryan Nichols, 31, a 1998 graduate of Thomas More Prep-Marian High School residing in Kansas City. Both were reportedly members of the helicopter’s crew.

German Brig. Gen. Carsten Jacobson, a spokesman for the U.S.-led coalition, told reporters troops had secured the crash site in a rugged area of eastern Wardak province and nobody was being allowed in or out of the area while the investigation was ongoing.

Jacobson said the coalition still had not yet determined the exact cause of the crash, but some officials have said the heavy and lumbering transport helicopter was apparently shot down. Officials said the helicopter was hit as it was flying in and approaching the area.

“We are still investigating this incident so we have no picture of what was the cause for the incident. That is what the investigation is basically all about,” Jacobson said.

The helicopter was ferrying a group of Navy SEALs to reinforce a group of Army Rangers who were under fire. It remains unclear if the Rangers and SEALs were taking part in a night raid to capture or kill an insurgent leader.

It was deadliest single loss for U.S. forces in the decade-long war.