I’m wondering if the PD’s concern is at least partially due to the fact that the leaker has likely seen all the rest of the pages of this journal.

Could there be references in there to individuals who had a hand in (deliberately) influencing this young woman to go on her violent rampage? Any number of DS minions - including government officials and/or FBI, C_A or others - could have been complicit and would be likely to do a runner or be seen as a liability by DS puppet masters and eliminated. Just a possible scenario.