Intermittent Stating Problem

I'm hoping someone else has encountered this and has some idea what might be the problem. I have a 2002 325ci that intermittently won't start. It happened again a couple of days ago. The car started just fine first thing in the morning. Drove it to work-no problem. Started again at lunch when I went to run an errand. Not out of the car two minutes, come back and it won't start. Cranks just fine. Tries to start and dies immediately. Left it to sit over night. went back the next morning to try one more time before I have it towed and its starts right up. This is the second time it has happened and both times after waiting an extended period of time it starts just fine. Any ideas about where to start troubleshooting would be greatly appreciated. Thanks.

Failing fuel pump is your best candidate without logical diagnosis. Less frequently a fuel filter.
Could check the pressure and flow rate at the fuel rail or replace the pump if it's years old. Do a filter soon too.
Get part number and shop using www.furiousmethod.com if you can DIY. Many vids on youtube.
Usually Bmaparts.com has great price.

Fuel, air and spark are your three troubleshooting friends.