Sorry to hear about the losses. What in the world did he do? Pour Windex in the tank? There isn't much you need to do in 48 hours. They would have been fine for that short amount of time.
Where these new fry by any chance? If so, he may have done nothing wrong at all. Sometimes fry don't make it.
If it's any consolation, I went away for a week and left my brother in law in charge of feeding my fish. He left the top up after feeding one day on one tank and my Asian arrowana (since I no longer have one I can mention it without worries
) jumped out and dried up on the carpet. Talk about a major financial loss of an irreplaceable fish.
Nowadays, I NEVER allow anyone to take care of my animals even for short periods of time (kinda explains why it's been 8 years since my last vacation
).