Ransom in the call-box
The son of a rich man was kidnapped. The kidnapper wanted the rich man to bring and put the expensive diamond into the call-box located in a city park. Policemen surrounded this park, intending to catch the criminal. The father of the kidnapped child came to the call-box and did everything the kidnapper said to him, but the police could not prevent the cunning criminal from taking the diamond out of the call-box. They didn't grab the villian as well. What did he do?