Police were investigating an apparent fatal shooting Thursday night in Charlestown. A white sheet was covering what appeared to be a body on the sidewalk on Monument Street at about 11 p.m. Boston police officers, state troopers, and Boston Housing Authority officers were on scene, along with several bystanders. Investigators at the scene declined to comment. Spokesmen for State and Boston police were releasing no details on the incident late Thursday.Travis Andersen can be reached at firstname.lastname@example.org. Follow him on Twitter @TAGlobe.