Population in the Mon Valley had soared with the arrival of immigrant labor, and so did crime. Anarchists took the blame for some of the arson, assault and murder in the Mon Valley in the first decade of the century. Since President William McKinley was assassinated by anarchist Leon Czolgosz in September 1901, the native population was highly suspicious of the political leanings of the foreign-born. Blame also fell on the Italian Blackhanders, and sometimes the two elements and their motivations were confused.