I expect that in hindsight they probably wish they had never confessed now as it would have no doubt been easier all round for them and for the cats owners who although distressed would have got over it in time, now that they have a focus for thier anger & grief it is different.
Putting myself in thier position if i had only just moved there recently and had no idea who the cat belonged to i would probably just bury it if it had no id, i mean lets be realistic - how many people take dead cats they have never seen before to be scanned & checked for injuries etc?
Sure i'd be right pissed off if it were my cat too but i would be even angrier if i found out someone knew it was my cat and didn't tell me - these people didn't know who's cat it was until afterwards & that should be taken into account i think, it's not like they murdered it, they weren't even there themselves when it happened.