SAN FRANCISCO — The director of the zoo where a teenager was killed by an escaped tiger acknowledged yesterday that the wall around the animal’s pen was just 12 1/2 feet high — well below the height recommended by the accrediting agency for the nation’s zoos. The San Francisco Zoo director, Manuel Mollinedo, also said it is becoming clear the 300-pound Siberian tiger leaped or climbed out of its open-air enclosure, perhaps by grabbing onto a ledge. “How she was able to jump that high is amazing to me.” Mr. Mollinedo said investigators have ruled out the theory the tiger escaped through a door behind the exhibit. According to the Association of Zoos & Aquariums, the walls around a tiger exhibit should be at least 16.4 feet high. But Mr. Mollinedo said the nearly 70-year-old wall was 12 feet, 5 inches, with what he described as a “moat” 33 feet across.