I also don’t know why “para perseguir a los responsables” wasn’t accepted as it means the same thing.

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Accepted Answer

Hola Susan
That could have also been used and would mean pretty much the same. We haven't included that option with the infinitive because the translation in English is saying "and toughen the law so that those responsible are pursued." The most accurate Spanish sentence here would be using "para que..." (so that...) and the use of a passive "se persiga/sean perseguidos", reflecting the passive in the English.
But, as David was saying, we do simplify this sometimes and use the more direct and simple para + infinitive. It wouldn't be that accurate and emphatic but it is pretty much saying the same thing. 
Saludos
Inma

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It doesn't quite mean the same thing. Para que means so that and it takes the  subjunctive.See lesson for reasons why - Using adverbial clauses para que, antes (de) que, hasta que, con tal (de) que, etc. + El Presente de Subjuntivo (present subjunctive)

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There is sometimes flexibility in allowing the [simpler] construction - using just the infinitive instead of the more formal "para que + subjunctive". In fact, with some verbs you occasionally see it even when there is a change of subject in the sentence. I am inclined to think that a lot of Spaniards would regard “para perseguir a los responsables” as acceptable >

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However, that^ infinitive construction would of course not carry the same pointed emphasis as using "para que ..."