Based on true events, a lonesome Sheriff’s lieutenant takes a supernatural, spiritual journey while attempting to unravel a conspiracy involving unsolved murders and missing persons and, in the process, has his cynical worldview turned upside down.

In all iterations of the logline thus far, the protag is described as being rather passive and emotionally disconnected. If it were me and my wife/girlfriend was killed, I'd be out there kicking ass to find the culprit - the rhetoric in a logline is as important as the details.

What specifically MUST he do as a result of his loved one's murder? Stop the cartel? Prevent others from being killed in the same way? His motivation to react to the event must be crystal clear.

My try:
After a satanic drug syndicate murder his wife, an atheist sheriff must team up with a preacher's daughter and the DEA to stop them from killing again.

Okay, I am going to give this another try, hopefully, this logline attempt is closer than my last one.
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"When his girlfriend (Love interest?) is ritually murdered, an atheist?sheriff is forced to team with the local preacher's daughter and the DEA, in order to follow the dark trail of a satanic syndicate, involved trafficking and human sacrifice."

Most stories are remarkably simple when you actually break them down. Even films that seem incredibly complicated, such as Christopher Nolan's Inception, can still be reduced to a simple spine of story.

With this in mind, I'm struggling to understand what everything that happens with the brother and drug cartel has to do with his quest for the girl. You said that it's the romantic pursuit of the girl that takes the protagonist on a supernatural journey - this journey being what forms the basis for your logline - ?but this has nothing to do with the the brother, the drugs cartel, or indeed the unsolved murders and conspiracy which wasn't really covered by your synopsis. It's a simple love story.

What are the true events? The way you've written some things sounds very much like they are pure fiction. Which bit's true?

I feel like there are two completely different stories being told (based on your synopsis) and I can't see (yet) how they are related. Firstly you need to decide what his primary goal is, is it to get the girl or to save his brother? That then gives you something to use for your inciting incident. There needs to be coherence between all the elements ?- the subplots must affect the main plot in some way. The logline, however, must focus on the main plot. Tell us his primary goal, what happened that started his journey towards this goal and what antagonistic forces he's working against. ?As far as characteristics go, if you tell us he's lonely but the logline doesn't suggest a love interest then it doesn't really give us anything. BUT tell us he's straight-laced or by-the-book combined with a plot to do with finding out his brother is a criminal and suddenly we can see where this guy is going to go.

Hope this helps.