Pretty much this: https://en.wikipedia.org/wiki/Streisand_effect
Also, govt (democratic ones, esp) are notorious for being short-sighted and taking populist measures, so no surprises here: http://en.wikipedia.org/wiki/Bread_and_circuses
Imo, what the govt should considering doing (if they haven't already):
1. Weed out rouge elements (sadly, extensive surveillance is one way to achieve this, another would be with help of citizen-journalists/investigators) within the state, and secure immigration points
2. A focused task force to address internal threats and give them a degree of autonomy.
3. A memorial to immortalize the victims.
4. Govt mandated security at places of congregation of all sizes (malls, stations, places of worship, parks).
Edit: /s