The rifle supposedly used to shoot Harrow is identified in dialogue as a ".276" and a "rare caliber," both factually correct statements, and the rifle shown is a Garand rifle, which was indeed chambered in .276 Pedersen in its earliest forms. However, the last T3E2 Garand sold at auction went for over $172000 USD, making the suspect's acquisition of it rather, well, suspect.
The title should be Ab Imo Pectore meaning "from the bottom of the heart".
Set to release in Australia on the 12th of May 2019