Rob Reiner and Son Nick 'Got in a Big Fight' at Conan O'Brien's Party Hours Before Murders: 'He Was Freaking Everyone Out'

Rob Reiner and his son Nick Reiner got into a heated argument at a Saturday night holiday party the night before the director and his wife Michele Singer Reiner were killed on the afternoon of Sunday, Dec. 14, multiple sources at the party tell PEOPLE.

TMZ first reported on Monday that Reiner, 78, and his 32-year-old son got into a "very loud argument" at a Christmas party hosted by Conan O'Brien on Saturday night.