Stolen iPhones disappeared in localize my iPhone

My 16 years old son claims that he has lost 2 iPhone 5s running iOS 9.2 during a month.

Both IPhones were set with localize my iphone and when i tried both time to localize them, i got a message saying that the iphone was desactivated and soon after the device icon vanished.

My guess is that my son has given both lock screen and iCloud password to do that.

It should require a hack both on the server and phone side to have that, shouldn't it ?

Thanks for sharing experience , i'm afraid that he´s in trouble and i would like to call the police if it is obvious that he couldn't lost them.