Who sent this letter? Fang Zheng didn't need to think to know.
The reason is simple. He's planted a spy on Belmod.
He can even see Belmod when she's taking a bath!
Fang Zheng even knows Belmod's plan—she wants to use this letter to lead him away, since she sent similar letters to Kogoro Mouri and Edogawa Conan. In Belmod's view, since Fang Zheng is a senior advisor to the Metropolitan Police Department, he's certainly not going to sit idly by when encountering such matters…
Well, actually Fang Zheng would keep out of it, especially considering that if Conan and Kogoro Mouri would really go, he'd just find a cinema and watch a movie.
