Steps (if you decided to catch the murderer by yourself)
If Calixto Corrium does not attempt to murder Arivanya even after 8PM:
1. Sneak up nearby.
2. Wait for 10PM just to be sure.
3. If that doesn't work, sleep until next day and come back.
4. If that didn't help, try below console command (press the key right below ESC key):
setstage MS11 130
This will trigger murderous action as soon as you close the console, so seize Calixto before he kills Arivanya. (I failed however)
If you couldn't save her, you can still stop him from going into the house.
Follow him (useful if you have Footprints mod) back to the house in question, and attack him vigorously until he drops dead.
If you were too late and he already went into the house, just prepare melee attack and shouts, and kill him after you come into the house.
(You can purchase house later, if you want. Useful if you have DLC called Hearthfire!)
Steps (If you got the former suspect into trouble and your previous quest failed)
Wait until Calixto is supposed to murder someone else.
If he is just wandering around not killing anyone, issue this command:
setstage MS11b 130
