Upon being released from prison and sympathetically handed money by the lieutenant—a ruthless man who has killed innocent villagers to get his hands on the last Catholic cleric in the state—the priest calls him a good man, and he means it. The lieutenant doesn't know he has the priest in his power; he knows only that an old man captured with illegal booze has no money and no prospects for work. He offers a kindness.
This isn't a moment of redemption for the murderous police officer, but it is a detail about his character that you shouldn't overlook. The lieutenant really does care about the poor. He's not a politician who speaks adoringly of the masses while doing next to nothing. Rather, he's an idealist who would wipe out much of the world to diminish their suffering.
Oh, he'll kill a few of his favorite people from time to time—when it's necessary for the greater good—but you really get the sense that these murders sadden him. Whatever else the lieutenant is, he's not insincere.
We don't learn exactly what happened to the lieutenant as a child that so motivates him now, but whatever it was, he hates the Church with a vengeance. We're talking the Viper's disdain for the Mountain, for you Game of Thrones fans…or Kahn's wrath at Kirk, if Star Trek is more your nerdy pleasure.
Take these sentences from the novel:
Something you could almost have called horror moved him when he looked at the white muslin dresses—he remembered the smell of incense in the churches of his boyhood, the candles and the laciness and the self-esteem, the immense demands made from the altar steps by men who didn't know the meaning of sacrifice. (1.2.24)
It seemed to him like a weakness: this was his own land, and he would have walled it in if he could with steel until he had eradicated from it everything which reminded him of how it had once appeared to a miserable child. He wanted to destroy everything: to be alone without any memories at all. (1.2.49)
This is more than frustration with priestly hypocrisy: the memories of his childhood in the Church fill him with horror. That's a Heart of Darkness word there. Whatever happened to him then moves him now. And not lightly! The lieutenant really does want to destroy everything—at least everything associated with the Church. He believes the Church perpetuates the one great evil: suffering in the world.
The lieutenant hates others as well. He has no love for politicians and foreigners or even his boss. He's prepared to massacre all of them as well (1.4.129). In the meantime, he grudgingly tolerates them, but with signs of his disdain. When he visits the home of Captain Fellows to inquire about the priest, he waits for the captain in the sun rather than walk to him:
The lieutenant stood there like a little dark menacing question-mark in the sun: his attitude seemed to indicate that he wouldn't even accept the benefit of shade from a foreigner. (1.3.56)
And remember: this sun isn't a pleasantly warm ball of light. It scorches and kills—like a giant tanning bed in the sky. Oh, wait…
On a couple of occasions, the lieutenant insists that he's not a barbarian. He allows the priest time to offer absolution to the dying gringo. He tries to persuade Padre José to hear the priest's confession before the execution. He's capable of small mercies, even if he's also capable of massacres. In other circumstances, we might have taken him for a decent fellow.
He's also pretty mellow as far as his personality goes. On the outside, that is. Cool and collected, he doesn't have outbursts of rage or eruptions of glory. He makes an entrance calmly. Outwardly, the dude abides, even with a squall of horror and vengeance in his soul. We're not sure if this makes him more likeable or even more terrifying.