william ziegler convicted of capital murder for 2001 killing of russell baker .
was sentenced to death , but had sentence quashed on appeal in 2012 .
today pleaded guilty to aiding an abetting murder , and was sentenced to the 15 years he has already served , allowing him to walk free .
judge sarah stewart said warned him against being bitter at hearing .
also cautioned him that world is ` very different ' compared to 15 years ago .