Composer and session musician Peter Broderick is prolific. This soundtrack to this documentary film by Vern Lott and Jennifer Anderson is his ninth full-length since 2005. The subject of Confluence is a series of unsolved crimes in the Lewiston-Clarkston Valley of Idaho where the Clearwater and Snake rivers meet. The real-life premise is grizzly and baffling: five residents of the region go missing between 1979-1982; yet only three bodies are found, murdered in particularly brutal ways. The unfinished investigation centers on a single suspect who was never charged. Broderick's 13-cue score is eerie to be sure, yet while the film's subject matter is quite grim, these tracks don't get there all that often. These cues are mysterious, opaque, sometimes suffocatingly intimate, and melancholy. They never resort to standard true crime film tropes (aside from some of their titles). There is precious little in the way of dynamics shifting here. Pianos, strings -- played and scraped -- guitars, sound effects, field recordings, and sparse percussion populate these pieces. The depth of eeriness on the opening theme "The Valley Itself" is beautiful, if anything. A lone female vocalist -- Arone Dyer -- sounds like Liz Fraser wordlessly vocalizing in a 19th century American parlor, absentmindedly singing to a piano in the backdrop. From here, the music becomes, ever subtly, more mournful -- the languid piano in "The Last Christmas"; the gradual increase and decrease of drama from the strings and Dyer's layered backing vocals in "Some Fisherman on the River"; the raw, rural viola tinges in "She Just Quit Coming to School" interspersed amid fluffy, atmospheric sound clouds. The only track where any real tension occurs is "The Person of Interest" (the suspect has more of an identifiable theme than any of the victims). Rankled layers of strings, guitars, and piano and effects all collude in what amounts to a composition that could accompany a more minimally adorned chase scene in a thriller. Broderick sings on "The Old Time" -- the closer -- with Dyer. Because it is an actual song, it feels simultaneously out of place here while seamlessly summing up the dozen pieces that precede it. Music for Confluence may lack the usual highs and lows associated with film scores, but it more than compensates for them with its sad, yet lovely strangeness.