The Phoenix ticket was a Columbo Red Herring. He checked with the guy who'd inventoried everything from Dr. Rusk's belongings to verify it wasn't there before throwing it out there to all possible suspects and waiting to see if anyone took a bite. Mrs. Rusk passed, the coach's wife passed, that left the boys. They almost passed and then came up with their cockamamie story about the FBI blah-blah-blah. Columbo knew at this point he had his men (boys).