Five years after Oklahoma voters approved a measure to legalize the licensed cultivation, use and possession of marijuana for medicinal purposes, the state is home to a thriving cannabis black market that grows and ships large amounts of marijuana throughout the country.
 The black market cannabis economy has led to labor trafficking, prostitution and, in one case, the killing of four people.
 Chen Wu, a 46-year-old former worker at an Oklahoma marijuana farm at farm near Hennessey — a small town about 68 miles northwest of Oklahoma City — is accused of killing four other workers on Nov. 20 after demanding $300,000 be returned to him for his “investment” in the illegal enterprise.
 Local and state agencies routinely raid illegal grow operations and seize millions of dollars in illegally produced marijuana.
 At the farm near Coleman, authorities reported the seizure of roughly 20,000 illegally grown marijuana plants worth more than $30 million in street value.
 The farm was among several grow operations raided within a span of weeks two summers ago.