Another Patterson, or is it?

Finished "The Postcard Killers" by James Patterson and Liza Marklund. Yes, it had the Patterson look and the short chapters that he's famous for but other than that....I think it was all Liza. Not like his style. Took me till half way through the book to get into it at all. Hope this isn't a new series of books. It took place in Europe. A couple is traveling around Europe killing off couples and staging them to look like famous paintings from that area. They are being hunted by a NY detective whose daughter was one of the victims. His helper is a journalist who received one of the postcards that was part of the killers calling cards. Why do you need so many co-authors, Mr. Patterson?