From his wikipedia page:
“On October 16, 1972, Begich and House Majority Leader Hale Boggs, of Louisiana, were two of the four men on board a twin-engine Cessna 310 when the airplane disappeared during a flight from Anchorage to Juneau. Also on board were Begich’s aide, Russell Brown, and the pilot, Don Jonz.[11] The four were heading to a campaign fundraiser for Begich.
***
In November 2015, a Seattle Weekly story detailed the work of journalist Jonathan Walczak, who since 2012 has investigated the plane crash and subsequent events in an effort to determine the fate of the flight that carried Begich and Boggs.[19] Walczak created a podcast about Begich’s disappearance, which was released by iHeartMedia in the summer of 2020. The podcast, called Missing in Alaska, explored the conspiratorial ideas that FBI Director J. Edgar Hoover or Detroit mobsters operating in Tucson had assassinated Hale Boggs.[20]”
I was living in Anchorage when that happened. I don’t recall hearing any conspiracy theories relating to it at the time. But after so many years, and now knowing what goes on being the scenes in government, I wouldn’t discount anything nefarious.