Dean Naujoks plucked what appeared to be part of an airline seat out of the icy Potomac River just downstream of Ronald Reagan National Airport on Thursday. It joined a grim collection of finds including American Airlines branded sugar packets and a waterlogged landing gear checklist. Upstream, emergency responders and investigators continued recovery work at the scene of a midair collision that killed 67 people in the United States' deadliest aviation disaster in almost a quarter century. Naujoks is part of the Potomac Riverkeeper Network, a group that promotes clean water in communities along the river. Naujoks said in a video he shared with the Associated Press that he reported his finds to law enforcement after returning to his dock in nearby Alexandria, Virginia. More than 40 bodies have been pulled from the river as the massive recovery effort continued, law enforcement officials told The Associated Press on Friday. The officials were not authorized to discuss details of the investigation and spoke on condition of anonymity. Investigators have already recovered the cockpit voice recorder and flight data recorder of the American Airlines plane that collided with an Army helicopter as the plane was landing Wednesday night at Ronald Reagan National Airport next to Washington, D.C. Officials are scrutinizing a range of factors in what National Transportation Safety Board Chairwoman Jennifer Hommendy has called an “all-hands-on-deck event.” All aboard the two aircraft were killed, with officials examining the actions of the military pilot as well as air traffic control after the helicopter apparently flew into the path of the American Airlines jet. Air crash investigations can take months, and federal investigators told reporters Thursday they would not speculate on the cause. Authorities were still looking for the helicopter's black box recorder, Defense Secretary Pete Hegseth said Friday on Fox News Channel. Other factors in the crash, including the helicopter’s altitude and whether the crew was using its night vision goggles, are still under investigation, Hegseth said. Military aircraft frequently conduct such flights in and around the nation’s capital for familiarization with routes they would fly in case of a major catastrophe or an attack on the U.S. that would require relocation of key officials from the capital region.