Daniel Garofalo of Gilbert, AZ probably wasn't following his roommate, Zac Penton, on Twitter—if he were, he might have noticed that on August 20, Penton tweeted (and has since deleted) his desire to "viciously murder" his roommates. Unfortunately, on August 22, that's allegedly what Penton did to one of them.
The two were apparently involved in some sort of argument or fight that ended with Penton shooting and killing 41-year-old Garofalo in their home, after which Penton called 911 and turned himself in to police.
That one tweet might not have been particularly alarming for Garofalo anyway, since Penton seems pretty into shooting and guns in general. A quick search of Penton's Twitter brings up a lot of tweets that, in retrospect, seem pretty scary. Especially the one about how easy it is to buy a gun.
I need 2 boxes of 9mm stat.— Zac☭ (@Zac_Penton) August 16, 2016