I can just hope that the Costa Rica's police will do the job, and that the kidnappers will be found. But really awful news... A few things confuses me, if family agreed to pay, why was he killed? Did the kidnappers receive the money? I guess they had no intention of letting him go.... perhaps it would be possible to track down the transaction, if there was any transaction done at all.
it is still uncertain if the ransom was actually paid ( different sources claim different amounts ) but not until police confirms more detail we are left in dark.
But if indeed transaction was made in BTC then they can kiss the money goodbye.