The US needs to treat this as an act of war by a foreign military/government, not as a criminal act by people acting in an individual capacity.
If the US can identify the individual hackers, then they should be able to identify the physical location from which the military committed the acts of war and respond with the use of force as permitted by the UN Charter and international laws and norms. By responding with grand jury indictments the US sets a terrible and dangerous precedent and is telling foreign governments the US will not do anything in response to military based acts of cyber warfare.
If the US can identify the individual hackers, then they should be able to identify the physical location from which the military committed the acts of war and respond with the use of force as permitted by the UN Charter and international laws and norms. By responding with grand jury indictments the US sets a terrible and dangerous precedent and is telling foreign governments the US will not do anything in response to military based acts of cyber warfare.