“Isn’t there a statute of limitations to be considered here?”
To determine that, first you’ll have to figure out what statute they violated.
It appears to me there is no such statute and the DA just invented a new crime on his own, which violates the prohibition against bills of attainder and ex post facto laws, before we even get to the issue of statute of limitations.
That right there will get that DA, City, County and State one hell of a 42 USC 1983 suit against them - deprivation of civil rights under the color of law