Phoenix ? There were no unusual movements or signs of trouble in the moments before two news helicopters collided while covering an auto chase, killing all four people aboard, investigators said Friday.

The National Transportation Safety Board issued a preliminary report but made no conclusions about the cause of the July 27 accident that killed the two-man crews for KTVK-TV and KNXV-TV.

Witnesses on the ground indicated that the KTVK helicopter was relatively stationary and the KNXV helicopter “was maneuvering” when the collision happened, the report said.

The preliminary report said another pilot told the NTSB the two news helicopters were “positioned a reasonable distance apart” when he first noticed them.

He then glanced away and when he looked back, the news helicopters were closer together and “shortly thereafter, they impacted.”