Manuel Mollinedo, director of the San Francisco Zoo where the escaped Siberian tiger killed one man and mauled two others, acknowledged Thursday that the wall of the tiger’s den was 4 feet shorter that it is recommended.

The den only has 12 feet 5 inches tall than the 16 feet 4 inches recommended by the Association of Zoos and Aquariums, an organization that establishes the standards for animal facilities.

Mollinedo thought that the wall at the Lion House was of 18 feet, but in the investigation the facility was measured and the officials discovered that the wall was too short, the New York Times reports.

The size of the moat was miscalculated as well. It was thought to be of 20 feet wide and 16 feet deep, but in the investigation it was discovered that the moat is 33 feet wide and 12 feet 5 inches deep.

Referring to the wall, Mollinedo said: “In retrospect, it wasn’t sufficient. But prior to this incident, I felt very comfortable that the exhibit was safe.”

He said that when safety inspectors examined the wall which was built in 1939, they’ve never raised any questions about the size of it, ABC News informs.

He said: “When the AZA came out and inspected our zoo three years ago, they never noted that as a deficiency. Obviously now that something's happened, we're going to be revisiting the actual height.”

A separate investigation was opened on Thursday by officials from the Department of Agriculture, which under the Animal Welfare Act implements regulations for animal care in captivity.

Police and zoo officials continue their investigations on how a 4-year-old, 300-pound tiger, known as Tatiana, escaped from its grotto and killed Carlos Sousa Jr., and mauled the two brothers. The tiger was shot three times by police officers.

Zoo officials said that they will install cameras and “hotwire” fence in the Lion House in order to increase the safety in the facility.

Police believe that one of the two brothers was attacked first and then the other two yelled in order to distract the tiger. Afterwards the animal let go to its first victim and grabbed Mr. Sousa.