According to a statement released on Tuesday by the National Transportation Safety Board, a northern Indiana school district is partially to blame for a 2018 crash that killed three siblings crossing a rural highway to reach their stopped school bus in Rochester.

The wreck was caused by a pickup truck driver’s failure to stop for the school bus, despite the vehicle’s activated and clearly visible warning lights and stop arm, and a road warning sign for the upcoming school bus stop, the NTSB said in part of its final report into the Octotber 30th, 2018 crash.

However, contributing to the cause of the crash was the Tippecanoe Valley School Corp.’s inadequate safety assessment of school bus routes, resulting in a prevalence of bus stops that required students to cross high-speed roadways, the NTSB said. The agency also found there was no clear policy established by the district for school bus drivers to follow in determining when it was safe to signal students to cross a roadway.

The crash killed 6-year-old twin brothers Xzavier and Mason Ingle, and their 9-year-old sister, Alivia Stahl. A fourth child, 11-year-old Maverik Lowe, suffered critical injuries. The pickup’s driver, Alyssa Shepherd of Rochester, was convicted in October of reckless homicide, criminal recklessness and passing a school bus, causing injury. She was sentenced to four years in prison, though she is appealing her convictions.