Where did an unemployed college student get $15,000 for an arsenal? (updated)

The cost of the guns, ammo and equipment that James Holmes accumulated for his deadly attack was as much as $15,000. Before starting his graduate studies, Holmes worked part-time at a McDonald's. How did he come up with that amount of cash? Was this deadly massacre financed by student loans? Did someone else give him money?

(CBS News) Sources say investigators have found key evidence in dumpsters and trash bins outside of James Holmes' apartment, including a shipping label from an internet ammunition store called BulkAmmo.com.

Investigators also tell CBS News they have recovered a surveillance video of James Holmes picking up approximately 150 pounds of ammunition at a Federal Express outlet in Colorado.

They've interviewed a UPS driver who says Holmes had 90 packages delivered to his workplace on the University of Colorado medical campus.

And sources say over the past several months, Holmes spent about $15,000 as he was putting together his deadly arsenal -- guns, chemicals, explosives, and ammunition.

Update: The University of Colorado says shooting suspect James Holmes had a federal grant to study neuroscience.