Not everyone rounded up is a murderer or similar. Some were impressed into the gangs under threat of death (or death to family members), and may not have participated in severe crimes. So it is taking a good while to sort it all out, as some will eventually be released. But due process to avoid errors either way is important, and takes time.
As an example, a few months ago I was at a home for teen mothers in San Salvador. One 14 year old mother had grown up in a gang. Her mother had been seized from her family when she was ten years old. The gangsters made it clear they would kill her parents if she wasn't given to them. A few years later she gave birth to the girl I met. When the big roundup happened, all the adult gangsters were seized. Someone offered to take in the girl, but instead they made her a sex slave and trafficked her, then dumped her on the streets when she became pregnant. Sorting out her mother's culpability or lack thereof needs to be done with care and consideration.
I was not insinuating that due care for all circumstances should not be weighed & considered. But when you have men (or women) who personally commit such heinous acts, it is a disservice to the rest of the prison population to keep them alive, not to mention the rest of the population if they should somehow get out. This country doesn’t have a death penalty. Too bad.