A lung specialist took the stand Monday as the federal trial of three former Minneapolis police officers charged with violating George Floyd’s rights resumed after being abruptly suspended last week because one defendant tested positive for COVID-19. J. Alexander Kueng, Thomas Lane and Tou Thao are accused of depriving Floyd of his rights when they failed to give him medical aid as Officer Derek Chauvin knelt on the Black man’s neck for 9 1/2 minutes while Floyd was handcuffed, facedown and gasping for air. Kueng and Thao are also accused of failing to intervene in the May 2020 killing that triggered protests worldwide and a reexamination of racism and policing.