Officials in Sanford, Fla., on Monday refused to accept the resignation of embattled police chief Bill Lee Jr. over his handling of the Trayvon Martin shooting case

Lee, who temporarily stepped down from his post last month in the wake of his department's investigation of Trayvon Martin's death, had planned to permanently resign.

Lee  faced stiff criticism over the decision not to immediately arrest George Zimmerman, the volunteer neighborhood watchman who says he shot Martin, a 17-year-old African-American, in self-defense on Feb. 26 in Sanford, a suburb of Orlando.

Zimmerman was taken into custody and charged with second-degree murder April 11 after Florida Gov. Rick Scott appointed special prosecutor Angela Corey to take over the case.

In announcing his decision to temporarily step down on March 22, Lee said he stood by his department's investigation but said he decided to temporarily leave his post because he believed he had become a "distraction."

His department cited Florida's controversial "Stand Your Ground" law, which permits a person to use deadly force to prevent imminent death or great bodily harm without first attempting to retreat, as a reason for not apprehending Zimmerman soon after the shooting.

The six-week interval between Martin's death and Zimmerman's arrest sparked nationwide protests about perceived racial injustice.

Zimmerman -- who is part white, part Hispanic -- was released on $150,000 bail around midnight Sunday night.

The Orlando Sentinel reported that Zimmerman has formally pleaded not guilty to his second-degree murder charge and his attorney, Mark O'Mara, told ABC News that his client is waiving his right to appear at his May 8 arraignment.

Newscore contributed to this report.