I'm personally inclined to think it was the tanning process for the leather.

That said, and going on the basis it is the carpet, I strongly recommend 2X Ultra Bissell. It's supposed to be used with a steam machine, but I've even been able to get out dog pee stains (and smell) in my office/living room carpet with it. I use it pretty concentrated with not a lot of hot water and use the scouring part of a kitchen sponge. As far as chemicals go, to me it has a pleasant smell which goes away pretty quickly.

Biba