source: http://www.sbs.com.au/dateline/story/about/id/601221/n/Infected
A quick timeline for reference:
1932 Tuskegee study begins
1943 Penicillin discovered as effective treatment for syphilis
1946-1948 Guatemala study
1972 Tuskegee study ends
1997 Apology from Pres. Clinton for Tuskegee
2010 Apology from Pres. Obama for Guatemala