CNN reports that the feds can't trace/track the shooter's weapon:

The source, who was not authorized to speak publicly about the investigation, said the weapon is a Winchester Model 6, .22 caliber rifle -- a type of gun manufactured between 1908 and 1928 -- long before records were kept on gun purchases.

Authorities also were checking to see if the weapon had been used in any other crime, the source said.
Dang.