In "The Markenmore Mystery" (1922) by J. S. Fletcher, the chief constable was talking to two lawyers about Guy Markenmore who had been murdered two days ago after his meeting with two men at "Sceptre Inn", to which he had gone after a meeting with his brother and his sister.
“What puzzles me considerably,” observed the Chief Constable, “is—how did those two men who were with Guy Markenmore at the Sceptre come into and get out of the district unobserved? My men have already made the most exhaustive enquiries at every railroad station in the neighbourhood, and we’ve got hold of—nothing!”
“Strangers, too!” said Walkinshaw.
“How do we know that?” demanded Chilford. “There are a tidy lot of men within an area of twenty miles who might have business dealings with Guy Markenmore. His business here that night might have been just as much with those two men as with his brother and sister. Probably it was.”
“Grimsdale asserts that the first man was an American,” remarked Walkinshaw. “We haven’t a plenitude of Americans in residence about here. I could count them on my fingers.”
What does "His business here that night might have been just as much with those two men as with his brother and sister" mean here?
I know that it's a long phrase, but I can't get the general meaning of it.