Letters sent Thursday from the city attorney's office to attorneys for Amritpal and Kulbir Dhaliwal say an investigation by the city "has revealed no indication of liability on the part of the city and county."
The claim denials prepare the way for a possible lawsuit against either the city, which owns the zoo property, or the nonprofit San Francisco Zoological Society, which jointly operates the zoo with the city.
Attorneys Mark Geragos and Shepard Kopp filed the claims, seeking unspecified financial compensation, on behalf of the Dhaliwal brothers.
On Dec. 25, a Siberian tiger named Tatiana escaped her grotto at the zoo and fatally mauled 17-year-old Carlos Sousa Jr., also of San Jose, and seriously injured Amritpal, then 19, and Kulbir, then 23. Tatiana was then shot to death by police.
The claims contended the brothers suffered physical and emotional injuries from the tiger attack, and were subsequently defamed by a public relations firm hired by the zoo after the attack.
After the incident, San Francisco police conducted an investigation into whether Sousa or the Dhaliwals may have taunted the tiger before it escaped or whether alcohol was involved, and during the investigation took custody of Kulbir's car and both brothers' cell phones.
Police suspended the investigation without filing any charges Jan. 29.