In the video created May 11, Stair introduces two pistol-grip shotguns as "the twins" Mackenzie and Rachael and matter-of-factly describes how he needs to block the doors and who will be working the night of June 7.
Police stressed that the store was closed to the public when the shooting occurred, and that nobody else was inside at the time.
He ends the video pondering how to prevent something like this from happening again, and says to the camera: "you can't prevent it". "You can only endure it". According to WBRE, employees were stocking the shelves overnight.
District Attorney Jeff Mitchell is calling 24-year-old Randy Stair's attack at a Weis Market in Tunkhannock, Pennsylvania, Thursday "a mental health situation that utterly spiraled out of control".
On his Twitter home page, Stair wrote: "I had to die in order to truly live".
New York State Police on Wednesday arrested a student who is accused of posting a false school threat toward Harpursville High School on social media.
This incident comes three days after a "disgruntled" Florida man returned to a business he was sacked from in April, shooting and killing five former coworkers, police said. After the store closed Stair retrieved a duffel bag from his auto with the two shotguns, and began his attack.
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Still, the Pentagon has been developing contingency plans in case there's any interruption, defense officials said. Trump says the country has "historically been a funder of terrorism at a very high level".
Troopers said Stair texted his mother at 12:37 a.m. Thursday, and discussed journals he kept and how he wanted his remains disposed.
The store's phone was not operating on Thursday morning (Friday NZT), and a call to Weis Markets headquarters in Sunbury was not immediately returned.
Police have identified the alleged shooter as Stair, 24, of Ransom Road, Dallas. One witness managed to escape unharmed. State police expected to release more information once the victims' families were notified.
Pennsylvania State Police Troop P Commanding Officer Jonathan Nederostek gives a statement to the press as the State Police investigate the murder of three people and the suicide of the shooter at Weis Supermarket in Eaton Township, Pa., on Thursday.
Troopers responding to the shooting found four bodies and the witness, who reportedly called Wyoming County 911 dispatchers. Authorities believe a male killed two men and a woman before turning the gun on himself at the market.
Officials have released the names of those involved.