does not confirm if someone is a source or not, particularly in an ongoing investigation.

All of that is part of the investigation, which is ongoing.

The president made it very clear, we're not going to comment on an ongoing investigation.

We are not commenting on the specifics of evidence because it is an ongoing investigation.

important milestone in an ongoing investigation

This is a question relating to an ongoing investigation and we're not having any further comment on the investigation while it's ongoing.