He was a founding member of the Symbionese Liberation Army (SLA), an extremist group based in Oakland that was classified as terrorist by law enforcement.
It was known for murders, armed robberies and the kidnapping of heiress Patty Hearst after Wheeler and Siem left the group in October 1973.
Siem joined him as they gathered with Soltysik (known as Mizmoon) and Nancy Ling Perry, another white upper middle-class radical.
Although Wheeler and another associate, Joe Remiro, taught the founding SLA members how to use weapons, he was increasingly at odds at the direction of the group.
On 4 May 1974, months after Patty Hearst had been kidnapped by the SLA and they had conducted an armed bank robbery in Southern California, an article was published in The Pittsburgh Courier quoting Siem.