The phrase "widening probe" typically means that an investigation is expanding or growing in scope. It suggests that authorities are looking into more areas or aspects of a certain matter. Full definition
It is expected to consider widening the probe, according to a source, though commission officials would not comment. (newsday.com)
Sources have said that Percoco — who in January began working as a top executive for Madison Square Garden — is at the center of Manhattan US Attorney Preet Bharara's widening probe of potential corruption in a slew of upstate development projects. (nypost.com)
Lubin & Meyer Lawsuits Are At Center of Widening Probe into Concurrent Surgeries The Patient Safety Blog April 14, 2016 (lubinandmeyer.com)