How do we respond to a request to rework a letter detailing a resignation?

Q: “An employee recently resigned and wanted me to write a letter for his attorney to prove that he no longer works for our company. I hesitated to write the letter, however I did. The letter stated that he resigned from our company and gave the specific date of resignation; now his attorney wants another letter stating that he is no longer employed with our company and to leave the “resigned” portion out of the letter. Should I write another letter the way the attorney has requested, or just leave it as it has been written? His attorney has not personally contacted me regarding this matter.” – Tara, Texas