Talk to families of unjustified imprisoned people or to the people itself. His 'fixing' was done by basically imprisoning everyone, which just happened to be close to any suspect gang member. There where even cases where a mailman was imprisoned because he just happenend to deliver a parcel during a raid.
Yes, he fixed the gang problem for now. But at a high price – the loss of a fair justice system. He imprisoned 1.2 % of the total population in just 2 years.
I know that freedom vs security is a fine balance and once security suffers significantly, you are willing to give up quiet a lot of freedom. But since he just imprisoned everyone and their relatives, its only a temporary fix – unless he wants to imprison them for life.