Vincent Weiguang Li was born on April 30, 1968, in Dandong, Liaoning, China. He was the second of three children in his family. His father worked as a custodian, while his mother was a math teacher. Li was born prematurely and had some developmental delays, not walking or talking until around the age of five. He started elementary school at nine years old but later caught up in his studies.

At 19 years old, Li attended the Wuhan Institute of Technology, where he studied automotive engineering. He graduated in 1992 with a bachelor's degree in computing. From 1994 to 1998, he worked as a computer software engineer in Beijing. In 1995, he married Anna, a woman he met while working at a factory. His father later described him as a restless and stubborn man who frequently moved from job to job.

On June 11, 2001, Li immigrated to Canada under the Federal Skilled Worker Program. He became a Canadian citizen on November 7, 2006. In Canada, he took on various low-paying jobs in Winnipeg, including working at a church and a fast-food restaurant. He was known to be quiet and polite but struggled with mental health issues that were not properly diagnosed or treated.

On July 30, 2008, Li boarded Greyhound Bus 1170 in Edmonton, Alberta, traveling to Winnipeg. He initially sat near the front of the bus but later moved to sit next to Tim McLean, a 22-year-old carnival worker who had fallen asleep near the back of the bus.

At 8:30 p.m., while the bus was on the Trans-Canada Highway near Portage la Prairie, Manitoba, Li suddenly pulled out a large knife and began stabbing McLean repeatedly. The attack was completely unprovoked, and McLean had no chance to defend himself. The other passengers fled in terror, and the driver stopped the bus while locking Li inside. As passengers watched in horror from outside, Li decapitated McLean and held up his severed head. He then mutilated the body further and was seen engaging in acts of cannibalism.

The Royal Canadian Mounted Police (RCMP) arrived quickly and surrounded the bus, leading to a long standoff. Li remained inside, pacing back and forth, before attempting to escape through a broken window at 1:30 a.m. on July 31, 2008. Police officers immediately tasered and arrested him.

Li was charged with second-degree murder, but after undergoing psychiatric evaluations, he was found not criminally responsible due to schizophrenia. His trial began on March 3, 2009, and on March 5, 2009, he was officially ruled not guilty by reason of mental illness. Instead of prison, he was sent to a psychiatric institution for treatment.

Over the next several years, Li was granted gradual freedoms as doctors determined he was no longer a threat. In 2015, he was allowed supervised outings, and by February 2017, he was granted an absolute discharge, meaning he was released with no criminal record or restrictions. This decision outraged McLean's family, especially his mother, Carol de Delley, who became an advocate for victims' rights, arguing against the early release of dangerous offenders.