2001 Volkswagen Jetta Oil Leak After Oil Change

I took my car to get an oil change at Pep Boys. I noticed a couple weeks later there was an oil leak. This has been going on for at least 2-3 weeks now. I took it back to them and asked if they could check and see if everything was tight. They looked and said both the drain plug and oil filter were on properly.
Now it could be totally coincidental but my spidey senses tell me that the problem occurred there (at Pep Boys, when they changed my oil).

Any thoughts? And is there anyway I can insist Pep Boys takes care of this? I don't know for sure that they are responsible but this car NEVER leaked a drop in the 14 years I've had it. And it all of a sudden starts leaking oil right after an oil change.

Thanks in advanced.