SAN FRANCISCO — A California preacher who convinced thousands of followers the world would end has posted an online letter admitting he has no evidence of an impending apocalypse and will no longer predict global doom.

In a missive posted Thursday on his independent ministry’s site, 90-year-old Harold Camping said he was asking for forgiveness for his sin in predicting Judgment Day, and has stopped trying to pinpoint future dates.

“We realize that many people are hoping they will know the date of Christ’s return,” Camping wrote. “We humbly acknowledge we were wrong about the timing.”

Camping’s Family Radio International broadcasts his messages from the nonprofit’s headquarters in a squat building near the Oakland airport. In recent years, the organization spent millions of dollars — some of it from listeners’ donations — putting up thousands of billboards plastered with his prediction of the Rapture.

Marie Exley, 33, was among those who spent her own money to put up apocalypse-themed billboards in Colorado, and later met her husband while passing out Bible tracts in Japan.

The pair then traveled through Israel, Jordan, Lebanon and Iraq to publicize Camping’s prophecy and spent May 21 holed up in Montana waiting for the end. She said Thursday she was glad that the Christian preacher had admitted he didn’t know everything about the Rapture.

“Sure, I was looking forward to it, but it’s actually a blessing to reconnect with family and friends. It’s like hey, now I can be normal again,” said Exley, who is writing a screenplay about her experience. “It may seem like I drank the Kool-Aid, but I should have done more careful studying and been more cautious about what I was proclaiming myself.”

Camping, a retired civil engineer, had originally forecast that some 200 million people would be saved when the globe was destroyed, and warned that those left behind would die in earthquakes, plagues and other scourges until Earth was consumed by a fireball.

After May 21 came and went, many listeners were crestfallen, particularly those who had quit their jobs or donated some of their retirement savings or college funds to get out the word. Three days later, Camping revised his prophecy, saying that Earth actually would be obliterated on Oct. 21. He said a mathematical error also prevented an earlier apocalyptic prediction from materializing in 1994.

Several weeks later, however, Camping was hospitalized after suffering a mild stroke and spent several months recuperating.

Camping said he would instead concentrate on deepening his faith through rereading the Scriptures.

“God has humbled us through the events of May 21,” he wrote. “We must also openly acknowledge that we have no new evidence pointing to another date for the end of the world.”

No one at Family Radio would explain what prompted Camping’s decision to post the letter.

Michael Garcia, who has worked as Family Radio’s special projects coordinator, said he couldn’t say why Camping decided to post the letter, but said it had made more people aware of his message.

“I’m sure a lot of people heard about the May 21 message, and now they’re hearing about this too,” he said.