The China-WHO joint mission said it hasn't discovered the origin of COVID-19 after its investigation in Wuhan but that it is "extremely unlikely" the virus leaked from a lab there. Why is tracing the source so important, and what are the next steps?

Guests: 
Prof. Wu Zhiwei, Center for Public Health Research, Medical School of Nanjing University;
Einar Tangen, Former U.S. Prosecutor.