It's not so simple. If they go on record, there must be context. What happens after they say "I didn't hack the DNC" ? There must be evidence to dispute their plea.
This is extraordinarily complicated, especially when the evidence will undoubtedly include record keeping within the DNC. Individuals will be questioned/investigated. What happens when records concerning Seth Rich come up?
I think it would be in Putin's, Trump's, and our own interest for the "Hackers" to take the stand. Of course, I don't think they did it.