Three people were injured at a concert where rapper Lil' Flip was performing in Colorado on Saturday (20Apr13) after two men opened fire on the crowd.
The hip-hop star played at the 4/20 marijuana rally in the Civic Center Park in Denver, which descended into chaos when shots rang out.
A man and a woman were shot in the leg, while a third victim was grazed by a bullet. A dog was also hit by a bullet at the event.
After the incident, the rap star took to his Twitter.com page to write, "I am just grateful that no one was seriously hurt."
Police officials are now urging revellers to get in touch if they have any details which could help their investigation.
Denver police spokesman Sonny Jackson says, "Everybody in this world has a camera nowadays, so if anybody has any pictures that might assist us, we'd like those as well."
The 4/20 celebrations in North America stem from the cannabis culture's link to 4.20pm, the time when marijuana fans like to light up.