A station master has reportedly admitted giving the green light to one of the commuter trains that collided head-on in southern Italy.
But Vito Piccarreta said that he did not bear sole responsibility for the crash that killed at least 23 people, according to Turin newspaper La Stampa.
Mr Piccarreta said: "I let the train depart, I was the one who raised the signal."
But he said there was confusion along the single-track line due to delays and that Tuesday's disaster "wasn't only my fault".
It has been reported that two station masters are among those under investigation.
Prosecutors are also looking at the reasons for delays in adding a second track despite EU and national funding.