Do you have a car? Do you live in Jen's neighborhood? You may have noticed that gas prices are very cheap.
Looking for an answer to only this one tiny question, Jen questioned neighbors/drank 20 Icelandic beers/hid in trashcans/aimlessly drove a surveillance van through Pasadena. Here's an interview with Jen's neighbor Rob in which they list all of the suspects.
Prepare for a mystery as big as earth itself.