Explained: Why the US is investigating lab leak theory to unravel Covid-19 origins Explained: Why the US is investigating lab leak theory to unravel Covid-19 origins Virus researchers have not publicly identified any key new evidence that might make the lab-leak hypothesis more likely. But the theory is gaining momentum, and US intelligence agencies are collecting more information to unravel the mystery. advertisement UPDATED: June 9, 2021 19:53 IST Security personnel stand guard outside the Wuhan Institute of Virology in China's Hubei province (AP photo) Once dismissed by most public health experts and government officials, the hypothesis that Covid-19 leaked accidentally from a Chinese lab is now receiving scrutiny under a new US investigation.