A motorist sped through a pack of more than 100 cycling activists in southern Brazil, sending bikes and screaming riders flying through the air and landing on the asphalt in a scene captured on amateur video and posted online.
At least 40 cyclists were injured, with most suffering cuts and broken bones, but nobody was killed, authorities said.
Police said the suspect, whose they did not name, fled the scene on Friday evening in Porto Alegre. He was brought in for questioning yesterday after authorities found his abandoned car at the weekend.
The man claimed riders surrounded his vehicle and began beating on it, causing him to panic and fear for his life, police said. But the lead investigator in the case called that version of events "fanciful".
Inspector Gilberto Montenegro told Globo TV network's G1 website that the man could face charges of attempted homicide. Under Brazilian law, prosecutors can decide whether to bring charges only after police close their investigation, which may take 30 days. The man is currently free.
Cyclists in the Critical Mass ride told the Folha de S Paulo newspaper that no riders were threatening the motorist.
"He drove behind us for two blocks, and people were trying to stay calm. Then in the third block he ... floored it on top of everyone," Marcelo Guidoux Kalil said. "It was a scene of war, with twisted bicycles and people bleeding on the ground."
In the video, thuds and sharp sounds of metal on metal are heard as the car accelerates directly through the pack of cyclists.
Scores of riders and eyewitnesses screamed and urged bystanders to call police and ambulances as they began giving first aid to the victims.