A puzzle based on true story. Can you crack it....?

[(:Blue Desert:)]

This actually happened in Taiwan. But what? Read this:

A rich man's son was kidnapped. The ransom note told him to bring a valuable diamond to a phone booth in the middle of a public park. Plainclothes police officers surrounded the park, intending to follow the criminal or his messenger. The rich man arrived at the phone booth and followed instructions but the police were powerless to prevent the diamond from leaving the park and reaching the crafty villain. What did he do?

[Madhu]

May be the villain was also disguised as a police man and got away with the diamond