The National Transportation Safety Board is joining the investigation into last week's plane crash in the Titicus Reservoir in North Salem.

South Salem couple Val and Taew Horsa are believed to have been killed in the crash. Human remains have been recovered and sent to the Westchester Medical Center for identification, but family members say it was the couple who was on the plane.

State DEP and police divers have been searching the reservoir, using sonar on boats to check the water for the plane debris, and investigators are also walking the banks looking for any wreckage. Searchers worked through the weekend and pulled the back of the plane and a wing out the water.

State police were back in the air Monday morning performing a perimeter check of the reservoir. They've already spotted eyeglasses and clothing, and are looking for more items that could help the investigation.

DEP officials say the specialized equipment will allow them to bring the heavy pieces of wreckage up from the water -- including what they believe to be part of the passenger compartment. They say once they recover most of the wreckage, the National Transportation Safety Board will investigate the cause of the crash.