Whilst passing through an eerily quiet LHR before Xmas, I mentioned this very conundrum to the security check people as I was collecting my valuables. One of them said that it happens more often than you'd think. However one passenger had their brand new iPhone 11 (£1200 worth) stolen by 'someone' within the last few months who must have been several steps ahead. The security were able to look at cctv footage from various angles, identify the passenger/thief and apparently the aircraft that they were flying on was turned around after less than an hour and they were arrested upon landing and the phone (and it's important personal information) was returned to the distraught owner.