Victor Frasno thought God was on the other side of an Antioch lake, so he tried not once, but twice to get across, even though he could not swim.

God would help him reach the other side of the 80-acre reservoir, he told his older brother. The brother was also “chosen,” so he pulled him into the frigid water, too.

After a chaotic hour or so at the sprawling Contra Loma Regional Park, battling with his brother and sister-in-law in and out of the frigid water, Frasno drowned.

Authorities pulled his body from the lake at 11:20 p.m. Friday, 20 minutes after the first of a series of world-ending earthquakes were supposed to have begun, according to an Oakland-based radio evangelist’s Judgment Day prediction.

The world did not end, but investigators believe the highly publicized rapture proclamation — with more than 5,000 billboards worldwide and a caravan of believers spreading the word — helped push Frasno, 25, over the edge.

“I believe it probably had something to do with the rapture because this wasn’t his normal behavior,” said Detective Holly Sontag, who investigated the drowning for the East Bay Regional Park District police, which oversees the park.

The tale began late last year when the devout Frasno temporarily moved from Florida to the Bay Area. He spent weekdays with his sister in San Francisco and weekends with his brother in Antioch, Sontag said. He had no work and was to return to Florida at the end of the month.

Come Friday, as Family Radio President Harold Camping continued to insist the end was near and the rapture became a Facebook one-liner, Frasno, his 27-year-old brother and his brother’s wife went to Contra Loma park, sat on some rocks and spoke about religion, family and life.

“He started talking about God profoundly, but nothing abnormal at that point,” Sontag said.

Later that evening, Frasno’s behavior deteriorated. As he sat in his brother’s apartment, Frasno began watching UFO videos and quoting Scripture from the book of Ezekiel, Sontag said.

Frasno insisted on returning to the south Antioch park. His brother and sister-in-law, who were not identified, went with him, worried for his safety. The trio walked along the trail adjacent to the reservoir and his religious rants continued, Sontag said.

“He told his family that he now understood the Bible and that God was going to come to see him,” she said.

Frasno told the couple God was across the reservoir and he needed to swim there. He dove into the dark water.

His brother and sister-in-law, the only one of the three who could swim, jumped in to rescue him.

As he screamed Scriptures, Frasno told his brother they were both “chosen” and needed to speak to God.

“A brief struggle ensued, but they all managed to get out of the water,” Sontag said. “At that point it became a tug-of-war,” she said. Frasno’s sister-in-law was trying to keep him from taking her husband into the water.

The brother told his wife to run for help while he calmed Frasno, the detective said. The wife ran to a softball field and found help, as the brothers calmly continued walking along the trail toward the swimming lagoon where Frasno believed God waited.

“The brother said, ‘Let’s just walk there and see if God is there,’ ” Sontag said.

Suddenly, Frasno said: —‰’The trail ends here,’ ” and threw both of them back into the water, she said. As the brothers struggled in deep water, Frasno yelled: —‰’Climb on my back, God has given me the strength to go across,’ ” the detective said.

The brother managed to wriggle out of his shirt and out of Frasno’s grasp, clamber back on shore and run for help, Sontag said. He last saw Frasno quoting the Bible and flailing in the water about 15 yards from the shore.

Frasno’s relatives were unavailable for comment Wednesday, but Sontag said they were despondent.

“It’s a very sad situation,” she said.

No alcohol was involved, she said, and investigators are waiting for drug test results. Frasno was not on any prescription medication and had no mental illness history, she said.

Frasno was a “very religious individual,” but the family knew of no direct ties to Family Radio, she said.

All the evidence, particularly the timing, led investigators to tie his drowning to the Judgment Day hysteria.

“The family never said anything related to rapture, but our sense is that was probably what happened,” Sontag said.

A call to Family Radio headquarters went directly to voice mail with a message alerting media that questions about the May 21 Judgment Day prediction would be addressed only during its radio and television programs.

Emails sent to a Family Radio spokesman bounced back to the sender, and Camping’s home phone number was no longer in service.

Contact Matthias Gafni at 925-952-5026.