Eight service members were rescued by officials.
Both were riflemen with Bravo Company. "All eight missing service members are presumed deceased".
"It sank completely", said Osterman, adding that "the assumption is it went all the way to the bottom", several hundred feet below the surface, too deep for divers. The Marines have called off the search, which started late Thursday afternoon.
"It is with a heavy heart, that I made a decision to conclude the search and rescue effort", said Col. Christopher Bronzi, 15th Marine Expeditionary Unit commander.
All the Marines on the vehicle, which resembles a seafaring tank, were assigned to the 15th Marine Expeditionary Unit, which is based at Camp Pendleton, the largest Marine base on the West Coast of the United States, between Orange and San Diego counties.
"Our thoughts and prayers have been, and will continue to be with our Marines' and sailor's families during this hard time", said Bronzi.
The craft was one of 13 amphibious assault vehicles that had just completed an exercise.
Assisting in the search efforts were the USS John Finn, the USS Makin Island, the USS Somerset, and the USS San Diego.
Of the seven others who have been recovered, two sustained injuries and were taken to area hospitals.
With the assistance of helicopters, ships and boats, more than 1,000 square nautical miles were searched but it was determined that there was little probability of successful rescue given the circumstances of the incident, officials said.
All eight missing service members are presumed dead after a 40-hour search effort was unsuccessful.
The 15th Marine Expeditionary Unit said that they have notified all the families of the Marines and Sailor involved in the tragic accident.
The vehicle, known as an AAV but nicknamed an "amtrac", for "amphibious tractor" is used to take Marines and their gear from Navy ships to land.
"We know precisely where it went down because other units were literally right there with it", he said.
There have been 10 to 15 reported incidents over the past 20 years involving AAVs, with the most recent report involving a water-based fatality happening in January 2011.
In 2017, 14 Marines and one Navy sailor were hospitalized after their vehicle hit a natural gas line, igniting a fire that engulfed the landing craft at Camp Pendleton.