Around the time of the explosion, Lieutenant Iverson said, officers fired sponge and beanbag rounds at three people who had shielded themselves behind a length of plywood near a burned vehicle on the bridge. The three were thought to be acting suspiciously and refused orders to emerge, he said.
Officers saw someone roll metal cylinders to the protesters by the burned vehicle, Lieutenant Iverson said, and then heard an explosion. Afterward, he said, several protesters ran up, pulled a woman from under the vehicle and ran off. Three propane canisters were recovered from the vicinity of the explosion early Tuesday, he said.
Lieutenant Iverson said that officers did not use concussion or flash grenades at any time. Instead, officers used tear gas, pepper spray canisters and what are known as stinger balls, round grenadelike objects that spread tiny rubber pellets to try to disperse protesters, he said.
Mr. Wilansky said that doctors in Minnesota had removed fragments from his daughter's arm that he hoped could be used to find out what caused the injury and to hold someone responsible.
