Ishmael first meets Lieutenant Jabati when he and his friends roll up in Yele. They think they'll be safe there because the army is in control of this town and is actively fighting off the rebels. That's not exactly what happens.
It's clear that Lieutenant Jabati is large and in charge in Yele. He makes demands for soldiers and he gets them. To be fair, his methods are pretty brutal:
"Some of you are here because they have killed your parents or families, others because this is a safe place to be. Well, it is not that safe anymore. That is why we need strong men and boys to help us fight these guys, so that we can keep this village safe. If you do not want to fight or help, that is fine. But you will not have rations and will not stay in this village. You are free to leave, because we only want people here who can help cook, prepare ammunition, and fight." (12.23)
He's also a master manipulator. Once he recruits new soldiers and trains them, he wastes no time messing with their heads so that they will unquestioningly follow his orders. Some of these are classic techniques. He tells the children that they can avenge their families. He says the rebels are subhuman and don't deserve to live. He demonstrates brutality and then praises the boys when they follow in his footsteps. Oh, and he also supplies them with huge amounts of drugs and keeps a constant stream of war movies playing. Is there anything he didn't think of?
All this helps to keep the boys from questioning anything that is happening to them. Lieutenant Jabati makes sure their minds are always occupied and that vengeance is flowing through their veins so they can't start asking pesky questions like, "Should I be killing children younger than me on a daily basis?" He also knows how to build them up so they will feel like they're part of one big happy killing family.
The last time Ishmael sees Lieutenant Jabati is when the lieutenant casts off some soldiers to go live in the rehabilitation center:
"You have been great soldiers and you all know that you are part of this brotherhood. I am very proud to have served my country with you boys. But your work here is done, and I must send you off. These men will put you in school and find you another life." That was all he said; then he smiled and walked away, asking the other soldiers to strip us of our military equipment. (15.13)
And just like that, the boys are cast off without a second glance from Lieutenant Jabati. This is a man that Ishmael has grown to trust. Heck, even love. He was willing to die for him and this is all the send off that the lieutenant can give them. No wonder Ishmael is confused as he leaves his camp.
If we had to say one thing in the lieutenant's defense it's that he's trying to win a war. War is a messy business, but we're not sure that means it's okay to try to claim victory through any means possible. Recruiting children as young as seven? Brainwashing them? Making them into drug addicts? Yeah, the lieutenant is crossing a whole lot of moral lines. So, it's official—Lieutenant Jabati is a really, really, really awful person.