I would not assume that they "know they are infringing" - people/companies often really are 'surprised' at the verdict. Lots and lots of gray space in patents and other legal domain - e.g. what is obvious, what isn't? ...
In addition to what iwfal said in #msg-67343915, bear in mind that the two patents that MNTA alleges are infringed were not issued by the USPTO until Aug 2009 and Sep 2010, respectively; until then, Amphastar could not have known that it was infringing on another company’s issued patents.