Maybe im a class 8 retard (I am) but my understanding of firearms is that you can use the serial number to trace its EXACT providence. was it defaced? My thinking is that leaving the firearm behind means a level of obfuscation has taken place that can usually only be attributed to state actors.
Like follow my logic, if its just some bada-bitch like you or me that buys a rifle legally, there will be documents, footage of the purchase, all that. They would find you before the end of the day if you left the rifle there
So its been this long and they dont even have a lead beyond grainy photos dosent that mean this rifle was acquired by more exotic means?
Btw have they published what the exact make and model of the weapon in question?