The title is misleading. Palestinians still believe that Israel has poisoned Arafat, but some Palestinians from Arafat's inner circle have cooperated with Israel and facilitated the process. So, Dahlan could be involved as an agent of Israel in poisoning Arafat.
27 injured in fire, explosion at former air raid shelter in Hamburg, Germany (DPA)
from the article: Fatah: Ex-Gaza strongman Mohammed Dahlan poisoned Arafat