Mass Murder at Addison Apartments is the event that Sal Fisher established the mass murder to prevent the infestation of Red-Eyes from spreading.
The Infestation of Red-Eyes
When Sal returned home after his date with Ash, he received disturbing text message from Larry. When Larry didn't answer Sal's cell phone, Sal rushed to the treehouse behind the apartment building, only to find Larry's suicide note detailing the purpose of his actions: Red Eyes was starting to infect him.
Donning the Necrolight Guitar and requesting the assistance of Todd Morrison, Sal investigated the treehouse to find a single, empty alcohol bottle on the floor. Before a proper investigation could be made, Sal was teleported to the roof of the Apartment building, right by the Red-Eyes Capsule, by the Ghost of Alison Rosenberg.
With the help of the Ghost of Larry, Sal destroyed the capsule and (temporarily) freed the residents from Red Eyes' grasp.
Prior Sal's Arrest
Upon entering the room of Terrence Addison, Sal learned the truth. Red Eyes had made an effort to infect the building before, and succeeded in possessing all the members of the Addison clan and was halted only by a young Terrence who was able to fight off his influence long enough to slaughter his family and present him from spreading. The Endless One manifested inside Terrence and eventually overtook him and had been pretending to be him for decades.
Using the Nercolight Guitar, Sal killed the Endless One and briefly met the real Terrence Addison who gave him a most dreadful mission: Kill all who were under Red Eyes' influence or the shadows will consume the planet. After great deliberation, Sal conceded and butchered every single resident of the apartment building, including his own father.
After the deed was done, Sal left the building to be greeted by a horrified Ashley Campbell and the Nockfell Police Department.