That's one HELL of a leap there. Bigger than the leap the tiger made.
The zoo had tranquilizer guns: FACT
The SFPD commandeered the trank guns: FACT
Trank guns are nonlethal: FACT
The SFPD used said guns on the tiger: Reasonable Speculation
The tiger is dead: FACT
The cops shot the tiger with something more then a tranquilizer: Reasonable Speculation
Maybe the trank brought the cat down but did not totally disable it since the dosage is dependent on the target animal's body mass and the cops using the weapon were not trained in it's effective use. A groggy cat being only slightly less dangerous then a fully alert one, our brave man in blue mercifully dispatched the still dangerous animal, preventing further carnage.
Better?
Regards,
GtG
PS I still think the tiger got the bum deal in all this.
PPS FYI the tranquilizer used by vets is usually a derivative of nicotine alkaloid. A dose that will put a 120 pound white-tailed deer to peaceful slumber will kill an adult human.