HR already investigated. Putting the Chief Human Resource Officer in charge implies what the investigation will conclude: rouge employees. Because if it was institutional, the CHRO would be responsible.
Then again, it isn't a commitment to cleaning out HR beyond anyone there who says, 'Oh I think it is ok.' And the whole 'thinking' thing is a way of backing off under the cover of 'We don't want to be thought police.'
There's no taking of responsibility for what happened on his watch. No personal commitment to action. No promise of full disclosure. This is damage control and the fact that HR is in charge of investigating allegations against it suggests that the plan is cover up. The CEO sets the culture.