Source: The Chandler boy struck and killed Friday as he rode his BMX bike wasn't wearing the bright-orange helmet his big brother demanded he always wear. Friends say Aaron Arnold, 11, had accidentally left his helmet behind when he took a lunch break after a morning of riding at the Chandler Bike Park. He was headed to his favorite BMX shop. On Saturday, friends and family gathered at that shop, just yards away from the accident scene, for a car wash to raise money for a funeral they never anticipated. Police say 24-year-old Chandler resident Ronnie Chavez's pickup truck struck Aaron at about 12:45 p.m. Friday as the boy rode his bike across the street. Aaron was pronounced dead at the scene. Police say Chavez initially left the scene and abandoned his truck but returned with his father to speak with police. He was arrested on suspicion of failure to stop for an accident involving a death, a Class 3 felony. But the next day, the friends who washed cars and talked among themselves mostly talked about Aaron. "He was the coolest, toughest, most amazing kid," big brother Chandler Golden said. Golden, 15, introduced his younger brother to BMX biking about a month ago and the two had since spent hours riding together almost daily. On Friday, Aaron went to the bike park near Arizona Avenue and Warner Road with friends. Golden said he rushed to the bike shop when he learned about the crash. A police officer told him his brother had died. Now he tries to remind himself that the brother he has looked after will now be watching out for him. As Golden and his family mourned, friends hurried to put together the Saturday car wash. A longtime family friend called the bike shop where Aaron stopped for near-daily breaks from hours of BMX riding. Owner Tyler Coleman immediately agreed to host the event. Coleman was ringing up a customer on Friday afternoon and noticed Aaron and his friend in the distance. When he looked again, he said he only saw one bicyclist and immediately ran toward Arizona Avenue. He wanted to find a way to help the boy's family. "Everybody is pretty torn up from it," Coleman said. "BMX is just like a big family. He was like a little brother to all of us." So instead of repairing a flat tire for Aaron -- what seemed to be an almost daily occurrence -- Coleman hosted the Saturday car wash. Late Saturday, organizers gave the family nearly $8,700 in donations, Coleman said.