The search company says there's a straightforward explanation.
"Our Autocomplete algorithm will not show a predicted query that is offensive or disparaging when displayed in conjunction with a person's name."
That means the company won't suggest what SourceFed was looking for even when connected to well-known criminals. For example, "Al Capone crimes" and "Ted Kaczynski crimes" also fail to auto-complete on the search engine.
It's also worth noting that a search engine's auto-complete suggestions are not the same as search results. Users are still free to search for anything they want about Hillary Clinton or any other candidate.