In event chart:
Anything that has "cannot see" or "cannot be seen" signification.
Combustion. If authorities are combust, they are weak, they cannot see clearly (they don't understand the situation). If perpetrator is combust, not so good for not being caught still "hidden form sight, not able to be seen" may apply.
Aversion. Signs that don't aspect each other have also "cannot see each other" meaning. So, authorities and perpetrator in signs of aversion cannot see each other. Authorities are looking for perpetrator but they just never see him.
Aspects. No applying aspects = no contact, no interaction. No aspects between authorities and perpetrator = they never catch him. Additionally, if authorities have aspects with malefics = obstacles and difficulties for them.
Signs. Essential dignity, authorities in detriment or fall = they are incompetent, very bad at their job = lesser chance to catch the perpetrator.
Houses. Authorities in cadent or unfortunate house = unable to act. Perpetrator in angular house = free to act.
Combination of all above, the more, the better for not being caught.