In a conversation with journalists, Luzhkov said that a special fact-finding commission is doing work. It will study technical materials used in building the park, he said.
Luzhkov could not say what had caused the tragedy.
"It can be the design or the quality of construction," he said. Luzhkov did not rule out sagging of the soil.
"The reason is local. No act of terrorism can be traced," he said.
Luzhkov added that the police and the federal security service (FSB) are inspecting the pillars of the water park to find traces of explosives.