If you have kids or pets, I'd be concerned, as they really can carry disease and if rabid and bite, could be a problem. Being an escaped pet doesn't change his 'ratness'. Maybe get a 'Have-a-Heart' trap so you can rehome him far away if you want.

yep, either kill him or move him to the woods somewhere. rats are pack animals, so either more will come or it will go to find others. also "he" may be a "she" and before you know it you have 100 of them.

the problem with even a bachelor rat freed from human cages...

no one bothers to neuter their pet rats. and sooner or later, rat will find another rat. and in six weeks, there will be half a dozen little rats...and in as little as three months, there will be fifty of them.

Decon is good and if another animal eats dead rat, will not kill that animal. You do need to get rid of the rat as their droppings carry hanta virus.

If you are going to take action i'd recommend using a live-catch trap. Rats are very intelligent when it comes to traps. I have much greater success using live-catch cage traps on rats than I do using any other type of rat trap. Try using a trap that is at least 4-5 inches square. Set it in the area that the rat has been frequenting and use either peanut butter or dry dog food for bait. A trap like the one pictured in the link below would be perfect.

Here is a link that might be useful: Animal Trap

Call you local health department. Around my town they like to know about all rats and will take action against hem.