More than 20 letters among the 1,200 items stolen in Monday's mail robbery have been found opened and torn to pieces, Hongkong Post said yesterday. The mail destroyed after Monday's robbery included promotional letters addressed to various recipients in Po Tat Estate and Sau Mau Ping Estate, in Kwun Tong, from a variety of senders, a police officer said. 'It is not known whether any valuables were stolen from the letters. We will contact the senders to find out,' the officer said, adding that the robbers apparently had not touched cheque books in the two bags of mail. The mailbags were recovered in Fu Tei Pai village in Fanling around 6pm on Monday. That was about six hours after the two postmen were confronted by two robbers, sprayed in the face with an unknown substance and had the bags taken from them. The thieves escaped in a delivery van in which two other men were waiting. The van had been parked in the estate's car park for about three hours before the hold-up, police said. The officer said surveillance cameras had captured the four culprits, one wearing a face mask. 'We are trying to identify them,' the officer said. Detectives from the Kowloon East regional crime unit are investigating the case and nobody has been arrested. A spokeswoman for Hongkong Post said the police were keeping the 20 torn pieces of mail for their investigation, and that the other 1,247 items in the bags had been delivered to the two public housing estates. It is not known if all the mail in the bags has been recovered, since the mail is not counted before being sent out. On Monday, Hongkong Post originally estimated that the two bags contained about 1,100 pieces of mail. The spokeswoman said more than 2,000 postmen would be reminded to be extra cautious, to avoid similar incidents. Management would discuss security with the staff union and collect opinions on the matter.