Moderator: United Airlines
Join Date: Jun 2007
Location: SFO
Programs: UA LT Plat 2MM, Hyatt Discoverist, Marriott LT Gold, Hilton Silver, IHG Plat
Posts: 67,284
First your friend must return the other person's property -- to knowingly not to will generate a set of problems you want to avoid.
Then try to get as much information you can about how the other bag was returned -- what time, what counter, any physical description of the UA person, .... then go to the airport and ask for a baggage supervisor.