The memo — first reported by ABC News on March 18 and by The Washington Post and The Associated Press two days later — said the fight going on then over removing Schiavo's feeding tube "is a great political issue ... and a tough issue for Democrats."
"This is an important moral issue and the pro-life base will be excited that the Senate is debating this important issue," said the memo, which was described at the time as being circulated among Senate Republicans while legislation was being considered to place the Schiavo case under the jurisdiction of federal courts.
Martinez said in a written statement that he discovered Wednesday that the memo had been written by an aide in his office.
"It is with profound disappointment and regret that I learned today that a senior member of my staff was unilaterally responsible for this document," Martinez said.
He said he accepted the resignation of the staffer who drafted and circulated the memo. "This type of behavior and sentiment will not be tolerated in my office," he said.
Martinez did not identify the aide, but The Washington Post said he was the senator's legal counsel, Brian Darling.
"Until this afternoon, I had never seen it and had no idea a copy of it had ever been in my possession," Martinez said of the document. He had previously denied knowing anything about the memo and condemned its sentiments.