It's not all of a sudden. He had listened to these tapes before, but on listening to them again he could hear what could be the ghosts that Vincent was telling him he heard. That would support the claim that Cole can actually see dead people.

From Wikipedia:

At first, Crowe thinks Cole is delusional and considers dropping his case. Remembering Vincent, the psychologist listens to an audiotape from a session with Vincent when he was a child. On the tape, when Crowe leaves the room, Vincent begins crying. Turning up the volume, Crowe hears a weeping man begging for help in Spanish, and now believes that Cole is telling the truth and that Vincent may have had the same ability.

It's not all of a sudden. He had listened to these tapes before, but on listening to them again he could hear what could be the ghosts that Vincent was telling him he heard. That would support the claim that Cole can actually see dead people.

From Wikipedia:

At first, Crowe thinks Cole is delusional and considers dropping his case. Remembering Vincent, the psychologist listens to an audiotape from a session with Vincent when he was a child. On the tape, when Crowe leaves the room, Vincent begins crying. Turning up the volume, Crowe hears a weeping man begging for help in Spanish, and now believes that Cole is telling the truth and that Vincent may have had the same ability.

Because he feels guilty for not being able to help Vincent, and not wanting to make the same mistake again Dr. Malcom decides to trust that Cole is telling the truth.

Because that would support the claim that Cole can actually see dead people.

From Wikipedia:

At first, Crowe thinks Cole is delusional and considers dropping his case. Remembering Vincent, the psychologist listens to an audiotape from a session with Vincent when he was a child. On the tape, when Crowe leaves the room, Vincent begins crying. Turning up the volume, Crowe hears a weeping man begging for help in Spanish, and now believes that Cole is telling the truth and that Vincent may have had the same ability.

It's not all of a sudden. He had listened to these tapes before, but on listening to them again he could hear what could be the ghosts that Vincent was telling him he heard. That would support the claim that Cole can actually see dead people.

From Wikipedia:

At first, Crowe thinks Cole is delusional and considers dropping his case. Remembering Vincent, the psychologist listens to an audiotape from a session with Vincent when he was a child. On the tape, when Crowe leaves the room, Vincent begins crying. Turning up the volume, Crowe hears a weeping man begging for help in Spanish, and now believes that Cole is telling the truth and that Vincent may have had the same ability.