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.