Officers are still investigating exactly where and when the alleged knife was found.
Israeli leader says deportation from West Bank would "drastically reduce terrorist acts."
The attack on Nathan Graff has raised fears that the stabbing "intifada" has spread beyond Israel.
Investigations by the Bexar County Sheriff's office, Bexar County District Attorney's office, and Federal Bureau of Investigations (FBI) are ongoing.
Clancy, a 27-year Secret Service veteran and trusted insider, takes over a troubled agency as its permanent chief.
Police shot a man after he stabbed a 22-year-old Israeli student in the head.