WASHINGTON, D.C. — The National Transportation Safety Board (NTSB) released a preliminary report on Wednesday with a few more details on the school bus crash in Indiana that killed three students and injured one other, but has not identified a probable cause yet.

“All aspects of the Rochester, Indiana, crash remain under investigation as the NTSB focuses on determining the probable cause, with the intent of issuing safety recommendations to prevent similar crashes,” the NTSB said in the preliminary report.

The majority of the information in the preliminary report has already been released by investigators. On Oct. 30 at about 7:12 a.m., a 2014 Thomas Built Buses school bus was headed northbound on State Road 25 in Rochester, Indiana, and stopped to pick up students at the designated location. It was then that a 2017 Toyota pickup truck traveling southbound hit four students who were crossing the road in the dark, according to the preliminary report.

A 9-year-old girl and two 6-year-old boys were killed. An 11-year-old boy was taken by air ambulance to a medical facility to be treated for his injuries, according to the report. It was previously reported that the children were siblings.

The bus driver had deployed the bus’s warning lights and stop arm. The road is a two-lane highway at this location, and has a posted speed limit of 55 miles per hour. Two warning signs, one that says “Watch for School Bus” and another that reads “Left Curve” are posted for the road’s southbound traffic, the preliminary report notes. There is no lighting at the road at this location. A mobile home park is located to the west of the road.

The NTSB is still collecting information from the Tippecanoe Valley School Corp. on its student transportation policies, bus route planning, and safety issues related to students loading and unloading on high-speed roadways, according to the preliminary report.

To support this investigation, the agency is also investigating two additional crashes that involved school bus loading and unloading: one in Georgia, and the other in Mississippi.

The NTSB’s preliminary report is available here.