Which preposition to use with counterfeiter

at Occurrences 1%

How she enjoyed it, and said that she never dreamed that tenement people could be so happy; and she finally waxed so enthusiastic that she gave a silver half dollar each to four little newsboys crouching over the steam on a grating in Twenty-third Street, and when they cheered her and a policeman came along, we told the dear old soul that he evidently thought her a suspicious character, a counterfeiter at the very least.

Which preposition to use with  counterfeiter