Any Ideas?!?!?!

I have 2 male cats, both not quite a year old. I had them both neutured 3 weeks ago and both are doing fine. My cats are indoor cats and never go outside (I live near a busy road and dont want to take any chances). This morning my Hobbes somehow got out (Still not sure how) but I found him a few mintes later. Ever since he has come back into the house his buddy "Iggy" is trying to kill him I Swear!!!!

They used to play fine, sleep together etc but now I have to seperate them. Iggy has always been more the aggressor and Hobbes is just a sweet mellow guy.

I am just wondering if maybe the smell on poor Hobbes is what is making Iggy so aggressive.

Any thoughts or ideas??? Any help would be wonderful!!!

Thanks

Hissy suggested this to me when my female was aggressive towards my male after a fairly invasive visit to the vet...Dab some vanilla extract onto both of their chins, behind their shoulders, and by their tail. This will make them smell the same and familiar to each other. This also happened when my Stinky girl fell off our deck and was outside stuck in a tree for hours. Tank was hissing and growling until I rubbed her down with these towellettes that we have.