July 4 shooting suspect a rapper with online footprint of violence

A 22-year-old man arrested after a mass shooting left six dead at a US Independence Day parade in a Chicago suburb had posted a variety of material online, some of it violent and also featuring former president Donald Trump.

Robert Crimo became the target of a manhunt in Highland Park after a rooftop gunman with a high-powered rifle turned a July 4 celebration into a ghastly scene. Firing into a parade, the shooter set off chaos as people ran. Around two dozen people, including children, were treated for gunshot injuries, with some in critical condition.

After a brief car chase, Crimo was taken into custody "without incident," police said.

Crimo bills himself as a musician with the moniker "Awake the Rapper." He was found to have posted disturbing material on various social media and websites, though they did not overtly reference politics or political figures except for two items about Trump.

In a YouTube video on January last year Crimo is with Trump supporters outside an airport. As a motorcade goes by Crimo flips his phone and shows his face, which has distinctive tattoos. He also tweeted a photo showing him draped in a Trump flag.

Crimo had his music on streaming outlets. An album released this year titled Brainwashed included songs Dead Again and I Am The Storm. A YouTube video posted eight months ago featured images of a young man in a bedroom and in a classroom along with cartoons of a gunman and people being shot.

A voice-over says: "I need to just do it. It is my destiny. Everything has led up to this. Nothing can stop me, not even myself."

Crimo last week posted a beheading video on a message board that carries depictions of murder.

The Chicago shooting is part of a wave of gun violence in the United States, where approximately 40,000 deaths a year are caused by firearms.

Two massacres in May saw 10 black supermarket shoppers gunned down in upstate New York and 21 people - mostly children - slain at a school in Texas.

According to the Gun Violence Archive there have been 311 mass shootings in the United States this year.

In another July 4 shooting two police officers were wounded after coming under fire at a fireworks display in Philadelphia.