DETROIT – The leader of a massive heroin, crack cocaine, and fentanyl operation in Detroit is headed to prison for 30 years. Officials said Demarco Tempo, who goes by Polo, was called “a McDonald’s for drugs” by former customers. Authorities said an investigation into a rash of non-fatal fentanyl overdoses and a fatal overdose in Warren led to an investigation in 2016. According to authorities, Tempo’s organization was selling heroin mixed with fentanyl, and sometimes just fentanyl, to people. Many of them were convicted on numerous charges related to distribution, conspiracy to distribute and other charges related to overdoses.