We execute people here in the US, but we've never officially put an innocent person to death in the modern era. Convictions get overturned and living people walk out of death row, but there aren't any posthumous pardons in living memory. In fact, states have successfully argued the public interest in preventing exculpatory evidence from coming to light. From Wikipedia:
In the case of Joseph Roger O'Dell III, executed in Virginia in 1997 for a rape and murder, a prosecuting attorney argued in court in 1998 that if posthumous DNA results exonerated O'Dell, "it would be shouted from the rooftops that ... Virginia executed an innocent man." The state prevailed, and the evidence was destroyed.
Relatives and supporters of George Stinney, the youngest person put to death in America in the last hundred years, are asking the state of South Carolina for a new trial. In 1944, an all-white jury convicted him of murdering two even younger white girls after only ten minutes of deliberations, and the sentence was carried out just 84 days after the crime was discovered. He was 14. At 5'1" and 95 pounds, it's been noted as extremely unlikely that he could have beaten the girls to death and carried their bodies to where they were found. He had alibi witnesses in his family, but was known to have spoken to the girls on the day they disappeared, and from that point on his fate was sealed.
This latest attempt at an exoneration is pretty much guaranteed to fail. There's so much about this case that truly shocks the conscience, but the institutional roadblocks are deliberately all but insurmountable. Hopefully, things in this country are going to change for the better.