The five were hit and killed by a passing train on the Milan-Turin line late on Wednesday evening.
The two survivors of the accident, the foreman of the team employed by a contractor and the Italian rail company RFI employee responsible for the worksite, have been put under investigation.
The latter, prosecutors believe, should have prevented the team of workers from starting work until after the train had passed.
The former, was leading the team of workers and escaped being hit by the oncoming train after seeing the approaching lights and managing to move onto the parallel track just in time.
Investigators are trying to work out why work was allowed to begin before there was confirmation that traffic on the line had been halted.
“It was a dramatic mistake,” Salvini said.
“The procedure is there.
“You can’t go to work on a track if there is no notification that no more vehicles are passing.”
ANSA