I can see substantial violations of the city's employment policies. Doing this sort of thing while "on the clock" certainly qualifies as a firing offense.

But were they off duty, or were the perpetrators "just plain folks", I'm not sure that a 'crime" would have been been committed, at least one in which the wheels of Justice are going to do much turning. Clearly, when the airline sells and continues to sell tickets on a flight for which all the seats have already been sold, it is risking financial exposure. Overbooking is a crap shoot based on odds calculated on the airline's experience on an individual route, time period or flight.

If you or I show up at the airport and make an evaluation that a flight is oversold, but a ticket and claim the compensation for a bump, that's not a crime. In essence, you and I would be betting against the airline's experience, risking our refundable ticket price, but not really much risk, since, were a seat to be available, simply not boarding and claiming the refund.

It's not a crime to do it twice or on multiple occasions, sharp practice, certainly, but unlikely to violate criminal statutes UNLESS (and here's the magic tripwire!) someone with the airline was cooperating in the deception, actually passing on info on over-booked/oversold flights, therefore creating a conspiracy to defraud, and actual fraud when the tickets was redeemed for compensation. This case sure sounds as if the police officers were engaging in the acts alleged during duty time, and seem likely to have had an accomplice with access to booking status.