A theory on the identity of the killer in The Little Things puts forward that it's the corrupt police officer, Deacon, who is responsible, and The Little Things ending has Reddit sleuths on the case. In the film's conclusion, Joe Deacon (Denzel Washington) and Jim Baxter (Rami Malek) have no answers to their murder mystery. Instead of solving his case, Baxter ends up murdering the prime suspect Albert Sparma (Jared Leto). Instead of turning Baxter in, Deacon conveniently helps him cover it up, just as Deacon's colleagues helped him cover up an accidental murder of his own years earlier.
https://screenrant.com/little-things-deacon-denzel-washington-real-killer-boots/