In-N-Out Shooting: Horrifying Surveillance Footage Released

Sickening new footage shows the recent mass shooting at an Idaho In-N-Out ... and it's tough to watch.

Surveillance from inside and outside the Twin Falls location shows the gunman opening fire last Saturday ... with customers and employees running for cover as the terrifying rampage unfolds.

It's difficult to stomach ... but the new footage shows the gunman -- identified as Chad Williams -- shooting an assault-style rifle inside the drive-thru window and at cars in the parking lot.

As we previously reported ... after the gunman opened fire, an armed civilian and off-duty officer shot back ... and you see the gun battle in this video.

The motive is still unknown -- and the suspect died by suicide.

Several people were injured in the shooting -- and 3 were killed, including In-N-Out employee Ashley Garibay, a 23-year-old from Stockton, CA who was working the drive-thru.

In-N-Out says Ashley was known for her warm personality and dedication to her job ... remembering her as someone who "strongly embodied our values" and greeted customers with "a smile and warmth that left a lasting impression on everyone she met."

The other victims were 66-year-old Dale Schultz and 59-year-old Christopher Claunch.