Investigators are poised to release evidence that could help clear up why an Amtrak train streaked into a sharp curve at double the speed limit and derailed last year.

The release, expected Monday, will be the first major development since the National Transportation Safety Board pinpointed excessive speed as a key factor within days of the deadly May 12 crash.

Investigators say the train was accelerating out of an 80 mph speed zone when it should have been slowing to 50 mph for the coming curve. It reached 106 mph just before the engineer activated emergency brakes.

The derailment left eight people dead and more than 200 injured. The lack of clarity on what happened has frustrated victims. Some have racked up more than $1 million in hospital bills.

Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.