NEW BRAUNFELS, Texas (CBSNewYork/AP) — Residents in the Texas town of New Braunfels are grieving for 13 senior adults who were killed as they returned home from a church retreat.

Authorities said Thursday that the First Baptist Church members who died in the Wednesday crash ranged in age from 61 to 87. They were returning home when the small bus they were traveling in and a pickup truck collided head on.

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Among those killed was the bus’s driver, Murray Barrett, who was a semi-retired middle school math teacher. Twenty-one-year-old Amity Dohoney said he’d taught her 7th and 8th grade math, and they remained close through the church.

The Texas Department of Public Safety reported Thursday the lone bus survivor remains hospitalized in critical condition, and the pickup truck driver is in stable condition.

On Thursday, federal investigators looked over the mangled remnants of the Dodge pick-up truck and Ford passenger bus as they tried to figure out what caused the two vehicles to collide, CBS’ Dion Champion reported.

“For reasons unknown, the truck veered into the southbound lane and truck the bus head on,” Texas Dept. of Public Safety Orlando Moreno said.

“We’re used to working fatal crash scenes. but first time that we’ve ever seen something like this happen with so many confirmed dead at one time,” he added.

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As the investigation began, churchgoers at First Baptist Church tried to make sense of the tragedy.

“Our church family is doing what church families do,” Pastor Brad McClean said. “They’re coming together, they’re crying together, they’re praying together.”

On Wednesday, McClean comforted people waiting for word on their loved ones.

“Their families are going to be hurting and our church family is going to be hurting,” McClean said.

Grief counselors will be on hand at the church through the rest of the week.

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(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)