Mainland police would have violated an agreement with Hong Kong police on cross-border investigations if - as claimed - they had raided the flat of a Hong Kong family involved in a corruption case, according to the Commissioner for Police. Eddie Hui Ki-on said in a reply to Democrat legislator James To Kun-sun that police had no information on the case revealed by lawyers defending Su Zhi-yi and his wife, Kam Shuk-yee, last month. 'If that had happened, their behaviour would have violated an agreement by the two sides,' he said. Figures cited by Mr Hui showed an increase of cases of assistance in cross-border police investigations since 1995, the year of the alleged raid. The number of mainland visits went up from 41 in 1995 to 100 last year, while cases of Hong Kong police visiting the mainland on investigations grew from 50 to 82. Mr Hui said investigations generally involved the collection of information, including interviewing witnesses, and the collection of evidence. Under Interpol guidelines, police officers must inform their counterparts of the nature of cases and the scope of assistance. Investigation work, including surveillance, must be conducted by local police. Su, 66, and Kam, 56, are standing trial in Zhaoqing, Guangdong, in a $4 million corruption case. Mr Hui said Su Suet, Su's daughter, had reported to the police on April 26 and given a detailed statement. She claims mainland police seized files from her parent's North Point flat in the 1995 raid.