Complex sentence: During the day a number of people, one of them former Union commander General George McClellan, became suspicious of the fact that the proclamation had been published in just two newspapers, and went to the offices of the "Journal" to determine the source.
Split into simpler sentences: During the day number of people, one of them former Union commander General George McClellan, got suspicious of the fact that the proclamation had been published only in two papers. They went to the offices of the "Journal" to find the source.