the lab leak theory is gaining new momentum. >> we know all laboratories all over the world have had and continue to have accidents despite our best efforts to prevent them. >> this professor penned a letter along with 17 other scientists writing, more investigation is still needed to determine the origins of the pandemic. both theories remain viable. now, the question is, will we ever know? it's not easy, if you think about it, tracing the origins of a small strand of genetic material on a massive planet never is. consider that it's been 45 years since the first recognized cases of ebola. yet we're still not sure of its origins. tracing sars to horseshoe bats