The military on Tuesday opened an investigation into a devastating helicopter crash that killed 30 U.S. troops and eight Afghans.

The probe was revealed as remains of the 30 American servicemen returned to the United States and were met by President Barack Obama, Defense Secretary Leon Panetta, Joint Chiefs Chairman Adm. Mike Mullen, relatives and other service members.

Pentagon officials would not discuss the details of the probe, expected to address a host of questions surrounding the Saturday crash in eastern Afghanistan, including a look at the insurgent threat and the instructions given to the special operations team crowded into the Chinook helicopter as it raced to assist other U.S. forces.

According to officials, the team, which included 22 Navy SEAL personnel, three Air Force troops, a five-member Army air crew and a military dog, was flying in to help U.S. Army Rangers who were going after insurgents on the ground. Seven Afghan commandos and an Afghan interpreter were also on board.

The helicopter apparently was shot down by an insurgent armed with a rocket-propelled grenade. It was the single deadliest loss in the decade-long war.

Gen. James Mattis, head of U.S. Central Command, has appointed Army Brig. Gen. Jeffrey Colt to lead the investigation. Colt is deputy commander of the 101st Airborne Division at Fort Campbell, Ky.

The helicopter crashed as it attempted to land in the Tangi Valley, a dangerous region in Wardak province, where coalition forces were engaged in a firefight with insurgents. The mission was targeting a Taliban leader believed to be in the mountainous and militant-riddled Sayd Abad district of Wardak.

The investigation will review a number of basic crash questions, more likely to rule out things like the weather, terrain and mechanical issues, since military officials believe the helicopter was shot down.

It will then also look at the altitude and flight path of the Chinook as it moved into the fighting zone. Chinooks are heavy cargo helicopters that do not have the agility of smaller, more maneuverable aircraft.

There also will be questions about why that team was called in, what they knew about the situation on the ground and what protections they may have had against fire from the ground.

The deaths have resonated in the United States because of the sheer number of casualties and because many of them came from the same Navy SEAL unit that killed al Qaida leader Osama bin Laden. None of the dead men was involved in that raid in Pakistan in early May.

Solemn ceremony
Two C-17 aircraft landed at Dover Air Force Base in Delaware between 10 and 10:30 a.m. ET, Defense Department spokesman Col. Dave Lapan told NBC.

Obama and top military officials joined families in witnessing what the Pentagon called the "dignified transfer" of remains at Dover Air Force Base in Delaware, home of the largest U.S. military mortuary.

A White House official said Obama at Dover boarded each of the two huge C-17 aircraft holding the remains and paid his respects and joined in a prayer, NBC News reported.

He then spent 70 minutes offering condolences to about 250 family members and armed service personnel.

Officials told NBC News that 20 cases containing remains were in one plane, 18 in the other. Fatigue-dressed soldiers brought the cases down red carpets as families and officials stood up from rows chairs facing the procession.

Journalists accompanying Obama were taken to a holding area away from the event.

There was be no public media coverage during the military ceremony because the badly damaged remains are mingled and still being identified, officials said.

Pentagon spokesman Colonel Dave Lapan denied there was any departure Tuesday from past policy.

"The instance that we have here is unidentifiable remains. So the families cannot give permission to anybody for media access to their loved one — because they don't know it's their loved one," Lapan told reporters at the Pentagon.

"They don't know with any certainty who is in that transfer case."

Obama's last visit to Dover Air Force Base, where the bodies of U.S. service members killed overseas come home, was in 2009 when he witnessed the poignant return of 15 soldiers and three federal agents killed in Afghanistan.

Fallen forces members of famous SEAL Team Six
Military officials said the troops in the crash were on a mission to assist forces pursuing a Taliban leader. NATO says the Chinook helicopter carrying the troops was shot down by an insurgent armed with a rocket-propelled grenade.

Ali Ahmad Khashai, deputy governor of Wardak province, said Taliban insurgents frequently move through the Tangi Valley.

"This area concerns us because many attacks in Wardak are organized and planned in Tangi," he said. "The enemy is active and the (military) operations have not been effective, unfortunately, because it is between three provinces. Maybe there are mountains and forests between these provinces that no one is taking responsibility for."

U.S. military officials said the helicopter was hit as it was trying to land.