If he had spent time in the archives, says van Pelt, he would have found evidence about ventilation systems, ways to introduce Zyclon B into these buildings--but of course I don't think he knows German so it wouldn't have helped very much.
All the research materials were on German that's why he did not bother spending time in the archives. 
mnli hypothesis: All the research materials were on German that's why he did not bother spending time in the archives.  premise: If he had spent time in the archives, says van Pelt, he would have found evidence about ventilation systems, ways to introduce Zyclon B into these buildings--but of course I don't think he knows German so it wouldn't have helped very much.