THE Kennedy Town landslide, which killed five people last month, was partly caused by a substandard retaining wall, the Canadian expert called in to investigate the cause revealed. Dr Norbert Morgenstern, who cautioned that it was too early to jump to any final conclusion on the Kwun Lung Lau Estate disaster, said yesterday that the one-metre thick wall would have been about three times the thickness if built by today's standards. He said that had it been three metres thick and collapsed it would have meant a slower deluge, possibly resulting in fewer or no deaths. ''You wouldn't build a wall like that today . . . and there are some questions of whether the thinness aggravated the slide. ''Had the wall been reasonably thicker it would have behaved in a more ductile way, giving warning [to people below],'' he said. Although it is unclear when the wall was built, it is believed to have been constructed in the 1890s. Acting Director of Civil Engineering, Dr Andrew Malone, said the estimate was based on old survey plans, and said the Government's investigation would try to find out when it was built and why. Dr Malone also agreed that the thinness of the wall ''may well have been'' a factor behind its collapse on July 23. His department, which began an immediate search for walls with similar characteristics, had not found any. But Dr Malone said tough modern standards by the Government meant new walls were ''perfectly safe'', and that older walls were being upgraded. Legislators voiced dissatisfaction that Professor Morgenstern's investigation would not determine whether anyone was responsible. United Democrat legislator Albert Chan Wai-yip said Hong Kong people would not be satisfied. But Professor Morgenstern said it would not be appropriate for him to go beyond the technical aspects. He said the ''technical message'' that he would provide would help find out who was to blame. Dr Morgenstern, who left the territory last night after five days of ''fact gathering'', added that his report - due out in late November or early December - would point out a number of other factors behind the collapse. Still to be studied was not just the ''obvious one'' of water seeping into the soil during the rains, but also water sources within the wall such as storm drains. A preliminary government report, published early this month, pointed to botched maintenance work combined with a leaking sewage pipe as possible causes. It found that the rainwater drainage system had been improperly connected to the underground sewage pipe at some time since the estate was built in 1965, increasing the amount of water flowing through the drainage network and the amount leaking out through holes in the pipe. The initial report also showed that a consultant had recommended eight maintenance measures in a study of the retaining wall and slope done a month before the collapse. Construction tenders were just about to be invited when the tragedy occurred. While not giving specifics, Dr Morgenstern said he and government geotechnical engineers had ''not seen exactly the same things'' in their investigations, but that their differences were expected. ''This is not abnormal in these circumstances,'' he said. Dr Morgenstern is to return twice in the coming months. He is being paid US$1,400 (HK$10,800) a day plus expenses. and is to complete his report at about the same time the government report is released.