UVALDE, Texas (CBSDFW.COM/AP) — A driver convicted in a church bus crash in South Texas that left 13 people dead will soon learn his punishment.

Twenty-one-year-old Jack Dillon Young, of Leakey, faces up to 270 years in prison after pleading no contest in June to 13 counts of intoxication manslaughter and one count of intoxication assault.

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The 12 bus passengers were all senior citizen members of First Baptist Church New Braunfels, who were returning from a three-day retreat in Leakey. The other person killed was the 67-year-old driver of the bus.

church bus crash (credit: CBS)

Prosecutors say Young was driving under the influence of a prescription antidepressant and had smoked marijuana before the March 2017 collision on U.S Highway 83 near Uvalde, about 75 miles west of San Antonio.

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His sentencing hearing began Wednesday in Uvalde.

Defense attorney Rogelio Munoz asked for mercy and said doctors didn’t properly monitor Young’s prescription drug use.

The hearing is expected to last at least through the end of the week.

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(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)