According to reports by Reuters, the engineer of the fatal train crash that killed 25 people and injured 135 was text messaging from his cell phone. It was the worst train accident since 1993. The Metrolink commuter train plowed into a Union Pacific freight locomotive on September 12 in Chatsworth, California.

A National Transportation Safety Board probe has focused on whether the engineer, identified as Robert Martin Sanchez, 46, failed to heed trackside signals. Sanchez was killed in the crash.

Cell phone records show Sanchez was sent a text message at 4:22:01 p.m., and received one at 4:21:03 p.m. The accident occurred at 4:22:23 p.m., according to Union Pacific train’s onboard recorders.

He received seven and sent five text messages between 3:00 p.m. and the time of the accident.

Sanchez also received 21 text messages and sent 24 while he ran a train from 6:44 a.m. to 8:53 a.m.

Since the timings were not all recorded on a common platform, the precise correlation between the events is not clear, investigators at the NTSB said.

Following the accident, California authorities temporarily banned railroad workers from using cell phones on duty.