USTER, Switzerland (AP) _ Investigators said Saturday they believed a weakened suspension system caused a concrete ceiling to collapse at a swimming pool, killing 12 people.

Mayor Walter Flach said federal experts were checking for faults in the stainless steel rods that held the 200-ton reinforced concrete slab.

Results of an official investigation are expected next week.

The roof remained intact when the ceiling crashed down on the three-pool complex Thursday night during a training session of the Uster swimming club. Five schoolchildren and seven adults drowned or were crushed in the disaster. About 40 people were in the building.

Police said the concrete ceiling was about 100 feet square and covered the three pools, including a children's wading pool, ''like a lid.''

''The main question is whether the collapse was due to the rods' rusting or to use of faulty materials,'' Flach said.

Ernst Waedensweiler, an engineer who helped design the 13-year-old complex, said Friday he examined some of the bars and found them to be rusty. He said this may have increased the load on the other bars, causing them to give way.