Star.

A:

As others very pertinently wrote above, one of the main reasons was political rivalry and struggle for power. Yet this is not the only reason that Krennic could be held responsible for the leak of the Death Star plans.
To understand why Grand Moff Tarkin acted this way, we need some further insight in his background. Tarkin grew up in an wealthy, aristocratic family but in an harsh Outer Rim planet, Eriadu. His family led the the seasoned Outland Regions Security Force, a paramilitary organization that provided security to the whole Eriadu system since the Republic was virtually absent in the Outer Rim. He had a  strict, almost military upbringing. When he became 16, as a ritual of passing, he was sent to survive in the untamed wildernessof Eriadu. He learned that his family has always been strong in defending Eriaduans first from nature and the wild beasts, then from pirates or any other threat. Tarkin grew up to be a decisive, calculating, unemotional, and ruthless man, who believed in order, stability, and devotion before everything else. He learned that as a Tarkin, weakness, indecisiveness, failure should not be tolerated, since they could mean death not only for him and his family, but also for the people of his planet. 
Director Krennic had come to represent all of the above in the eyes of the Grand Moff. As a Director of the Advanced Weapons Research, he failed to prevent a critical security breach, he failed to deal with it once it occurred, and he wouldn't