The Latest on a murder-suicide shooting at a Pennsylvania supermarket (all times local):

6:15 p.m.

A Pennsylvania supermarket employee who shot and killed three co-workers overnight posted a video online just before the shooting where he describes his plan in detail.

It's part of a long online trail prosecutors say 24-year-old Randy Stair left just before the killing at a Weis Market in Tunkhannock, Pennsylvania.

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.

He also laments what a tight timeframe he has to block the doors, post all his documents and video on social media and then kill everyone.

Police say Stair blocked store exits before killing three others and himself. A fourth co-worker escaped unharmed and called police.

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."

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3:50 p.m.

A prosecutor says a Pennsylvania supermarket employee who shot and killed three co-workers overnight appears to have left a long trail online, including a partially animated film he produced that praises teens who massacred students at Columbine High School in 1999.

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."

The bio on a Twitter account the prosecutor said is believed to be Stair's says he "had to die in order to truly live" and that he was "speaking from before and beyond the grave."

Police say Stair blocked store exits before killing three others and himself. A fourth co-worker escaped unharmed and called police.

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12:25 p.m.

Police say a Pennsylvania supermarket employee who shot and killed three fellow workers spent the first 90 minutes of his shift blocking entrances and exits so no one could flee once the shooting started.

At a news conference outside the Weis Market in Eaton Township on Thursday, state police say 24-year-old Randy Stair fired 59 shots from two pistol-grip shotguns he'd brought into the store in a duffel bag early Thursday.

Police say one witness inside the store managed to flee and call 911.

Police say Stair killed himself after shooting his three co-workers. It happened after the store closed for the night.

Authorities say it's still unclear why Stair targeted 63-year-old Terry Sterling, 26-year-old Victoria Brong and 47-year-old Brian Hayes.

Police are searching for a motive and are examining his online activity.

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10 a.m.

Pennsylvania police say a supermarket employee brought two guns to the store where he shot three fellow workers after the store had closed.

Police didn't immediately explain why they believe 24-year-old Weis Market employee, Randy Stair, shot three others before killing himself early Thursday at the store in Eaton Township.

They say Stair started working when the store closed at 11 p.m. and took two pistol-grip shotguns from a duffel bag he brought to the store.

They say he fatally shot three co-workers: 63-year-old Terry Sterling, 26-year-old Victoria Brong, and 47-year-old Brian Hayes.

Police say Stair fired random shots inside the store before shooting himself in the head. One witness managed to escape unharmed.

Troopers planned to release more information at a news conference.

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7:30 a.m.

State Police say four people are dead in a murder-suicide in a northeast Pennsylvania supermarket.

Troopers responded to a report of someone shooting people inside Weis Market in Eaton Township just before 1 a.m. Thursday.

Troopers found the bodies of three males and two females inside, along with one witness.

Authorities believe one of the males opened fire on the others before turning the gun on himself.

Authorities believe it is a contained incident and the public is not in any danger.

The investigation is ongoing.

No names have been released.