It's not about being merciful to Babalus. Once proven guilty she deserves punishment. Losing her post and jail time, I'd say. Execution would be too much imo.
It's about what
@CannibalShinobi said, that torture creates
false confessions. Torture someone enough and they'll start telling you what they think you want to hear, just to make the torture stop. And if you bring someone in for questioning, torture them, and they end up not being involved? That person and all their friends now hate your filthy guts. The better way is to ask questions over, and over, and over, see where the story changes, check their story against the facts, etc. If you have multiple suspects get them to tell the same story and see where the differences are. A lie will show cracks eventually. Interrogation > Torture.
But the second point is that Torture causes blowback. The US torture program under President Bush did not find many terrorists. But it did piss off the entire region and create more terrorism. It was counterproductive.