San Francisco officials say an investigation has found the city not liable for injuries suffered by two brothers attacked by an escaped zoo tiger.

In a letter released Friday, City Attorney Dennis Herrera denies claims filed by Kulbir and Paul Dhaliwal. A Siberian tiger mauled the men and killed their 17-year-old friend on Christmas Day.

Herrera says the claims should be referred the San Francisco Zoological Society, which manages the zoo, and to the society’s insurance company.

The claims are a precursor to a lawsuit. The Dhaliwals’ attorney says he expects to file one soon.