No clear culprit. No smoking gun. While COVID-19's origin story is currently defined by a lack of hard evidence and data, scientists around the world continue their search for answers to how the pandemic began. CNN Chief Medical Correspondent Dr. Sanjay Gupta speaks to leading virologists, epidemiologists and coronavirus researchers in "The Origins of COVID-19: Searching for the Source," premiering at 8 p.m. ET Sunday. As the world approaches the two-year mark since this novel coronavirus was first detected, there have been many twists and turns in the investigation into the origins of SARS-CoV-2, the virus that caused the pandemic. Some clues have led to dead ends, while others have spurred even more questions.