Murders in Sydney - Mathematics Professor Alfred Dunningham, PhD, #1

There are three murders in high-profile locations around Sydney, New South Wales, Australia, in one week, and each victim has a similar tattoo on his arm. There's no evidence of struggle; the news is front-page headlines, and the Police Commissioner is desperate to make an arrest. Unable to make any headway, the Police invite Mathematics Professor Alfred Dunningham, PhD, to come to Sydney to help them.
Besides teaching mathematics, he gives seminars worldwide on "Detective Work Made Easier Through Mathematics." He helps the Police make sense of the pieces of the puzzle; they find their suspect and arrest him. Sydney residents feel more at peace when the newspaper headlines announce the arrest. But another body is found, and it fits the same pattern as the previous murders. Do they have the right person in custody? The professor knows, and it's shocking when he names the real killer.