(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.