"This is the most painful decision I have ever made in my life," Robertson, 67, wrote in a letter to Eugene DePasquale, chairman of the York County Democratic Party. "But I believe it is the right decision for the people of the city of York and for the York County Democratic Party."
He is one of nine men who have been indicted in the slaying of Lillie Belle Allen, 27, who was gunned down outside a relative's car on Sept. 21, 1969.
Robertson, a police officer at the time, allegedly provided ammunition to members of a white gang that attacked Allen and other blacks. He has acknowledged participating in a white-power rally the day before Allen's death but maintains that he had no part in the fatal attack.
Allen and Henry Schaad, a white rookie police officer, were killed in weeklong rioting that also left 60 people injured and dozens of city blocks burned down.
A grand jury, convened when the case was reopened last year, recommended in April that 11 people be charged in Allen's murder. There have been no arrests in connection with Schaad's death, which is under investigation by a grand jury.
After Robertson was arraigned last week, a preliminary hearing was scheduled for today. It has been postponed and not rescheduled.
Of Robertson's decision to withdraw, DePasquale said: "[He and his advisers] came to the conclusion that he could not continue under this scrutiny. He made the right decision for the city and for the party."
He added that the party had not pressured Robertson to pull out. "It was his decision," DePasquale said.
Robertson wrote that he "would have loved to continue serving this city for another four years. . . . But I recognize that this is not possible. Someone else must now continue this work and lead this city toward the bright future it has earned."
The 20-member executive board of the York County Democratic Party is to meet this week to begin the process of choosing a candidate to run in November's election against Republican Betty Schonauer.
"We need to formalize the procedures to post the public notice and walk people through the process," DePasquale said. "We want to move with deliberate speed but do not want to rush to judgment."
He called Crenshaw, the primary challenger, a "very strong candidate" and said the board must consider all who meet the criteria. The plan, he said, is to name a candidate by July 1.
Crenshaw, who said yesterday that he lost to Robertson by 120 votes of about 7,000 cast, said he still believed the mayor should resign.
"Certainly, this will help get away from the negative attention the city has been having," he said of Robertson's withdrawal. "But it will not dissipate entirely, because he will still be around."
Robertson's announcement came on a day when local civil-rights leaders held a news conference to demand his resignation and withdrawal from the mayoral race.
Robertson's lawyer, Richard Oare, did not return phone calls seeking comment.
Amy Worden's e-mail address is firstname.lastname@example.org.