Pata Zoo has offered a 100,000-baht reward for information leading to the arrest of artists who spray-painted “Free Bua Noi” above the main entrance of the Pata Department Store in Bangkok.

The graffiti attack follows what the zoo called unfair criticism of its care of the 33-year-old gorilla Bua Noi by activist groups going back two decades.

The store will now take legal action against those who attack its treatment of the animal, the zoo said.

It said that over the years, many activists had defamed the zoo, which occupies the sixth and seventh floors of the department store building. Some had published photos of Bua Noi in her cage on the seventh floor, which the zoo said misrepresented its treatment of the animal.

Some wildlife conservationists had told school children that Bua Noi was tormented and asked them to support the “Free Bua Noi” movement, the zoo said.

Bua Noi was in the spotlight again last October when reports said that the government wanted to buy the ape for 30 million baht and relocate her to Germany, where she was born in 1990. Pata denied the reports and said Bua Noi was not for sale.