A married couple and their two young sons who were moving from Montgomery County to California were killed early Sunday in a fiery highway crash in western Nebraska.

Christopher Schmidt, 30; his wife, Diana Schmidt, 28; and their sons Samuel, 2, and Conner, 3, were publicly identified Tuesday night by officials in Nebraska’s Cheyenne County, near the state’s borders with Colorado and Wyoming.

The Schmidts had lived in the 900 block of Clopper Road in Gaithersburg for about a year and were returning to the Sacramento area, where they had grown up, said Diana Schmidt’s father, Brad Baumann, who lives in a Sacramento suburb.

Baumann said his son-in-law worked for the Energy Department and his daughter was a technician at the Maple Springs Veterinary Hospital in Potomac.

Cheyenne County’s chief prosecutor, Paul Schaub, said Diana Schmidt was seven months pregnant when she died. A truck driver involved in the crash has been charged with four counts of manslaughter, each punishable by up to 20 years in prison, and the lesser crime of vehicular homicide of an unborn child, Schaub said.

He said the Schmidts were traveling in two cars, one directly behind the other, when they were forced to stop in stalled traffic about 4:20 a.m. Sunday in the westbound lanes of Interstate 80 between the Nebraska communities of Potter and Sidney.

A tractor-trailer rig approaching from behind slammed into the Ford Mustang Christopher Schmidt was driving, Schaub said. The force of the collision propelled the Mustang into the rear of the Toyota Corolla carrying Diana Schmidt and the children.

The Toyota then crashed into a truck that was stopped in front of it, Schaub said. Both cars burst into flames.

“There was very little left of either vehicle,” Schaub said, adding that it took “many hours” for authorities to positively identify the four victims. He said the family’s three dogs also perished in the crash.

Baumann said his daughter and son-in-law met as children and married in 2005, while Christopher Schmidt was in the Air Force. Schmidt left the Air Force in 2010 and took a job with the Energy Department. The couple moved to Gaithersburg last October from the Northern California town of Olivehurst, Baumann said.

Christopher Schmidt recently got a job offer from the Social Security Administration that would allow him and his wife to return to their native California. Although the job offer was withdrawn for budget reasons, Baumann said, the couple decided to go ahead with the move, and they set out on a cross-country drive last week.

“They were coming home,” Baumann said.

The traffic backup that forced them to stop resulted from another fatal crash involving a tractor-trailer rig, about four miles to the west.

The truck driver involved in the crash that killed the Schmidts was identified by authorities as Josef Slezak, 36, of River Grove, Ill. He is being held in the Cheyenne County jail.

Schaub declined to discuss specifics of the charges against Slezak except to say that he allegedly was driving carelessly before the collision.

This item has been updated.