What happened next, captured by terrified onlookers on their cellphone cameras and later replayed in news reports, would shock the Chinese public and trigger an official crackdown on what Beijing has characterized as a dangerous doomsday "cult."
"Go to hell, demon," one of the accused, Zhang Lidong, yelled as he beat the woman with a steel mop handle, telling her she would "never come back in the next reincarnation."
Other members of the group threatened diners that they would kill anyone who intervened, reported Chinese state media.
By the time police arrived at the fast food outlet in the city of Zhaoyuan, in the eastern Chinese province of Shandong, they found the victim, a 37-year-old mother named Wu Shuoyan, lying in a pool of blood.
Zhang was kicking and stomping her while a boy beat her with the mop handle, state media reported; within the hour, she was pronounced dead at a local hospital.
Five adults have been convicted of murder over the attack on May 28, 2014 -- Zhang Lidong, Zhang Fan, Lyu Yingchun, Zhang Hang, Zhang Qiaolian. They are all members of the Church of Almighty God ("Quannengshen"), Zhaoyuan police said in a statement.
And on Monday, two of them -- father and daughter duo Zhang Lidong and Zhang Fan -- were executed in east China's Shandong Province on following the approval of the use of the death penalty by the Supreme People's Court.
After his arrest last year, state television broadcast interview with Zhang Lidong in his cell, in which he confessed to the killing but expressed no remorse.
"She was a demon," he said, telling the interviewer that he and his co-accused were members of the church. "She was an evil spirit."
Authorities said the accused were likely gathering the phone numbers to find potential new recruits when Wu's refusal angered them, state media reported.
Struggle with the 'great red dragon'
Also known as Eastern Lightning ("Dongfang Shandian"), the group preaches that Christ has been reincarnated as a woman from central China, and that the righteous are engaged in an apocalyptic struggle against China's Communist Party -- which they refer to as the "great red dragon."
Linked to kidnappings, violence and extortion, the group has been listed among 14 banned religious groups by China's Ministry of Public Security since 1995.
Emily Dunn, an Asian studies academic at the University of Melbourne who wrote her doctoral thesis on the group, said its illegal status had made it paranoid and secretive, with members often only knowing each other by aliases, so they could not incriminate each other if detained by authorities.
"It's about as illegal and politically sensitive as religion gets in China," she said. "As the government has cracked down more, Eastern Lightning's rhetoric has escalated against the government."
China's Academy of Social Sciences says there are now 23 million Christians in the country. But with many belonging to non-sanctioned, underground "house churches," experts believe the true number of Chinese Christians could be much higher.
Eastern Lightning, part of a tradition of heterodox, quasi-Christian religious movements in China, was estimated as having between several hundred thousand and one million members, said Dunn. It was viewed by Beijing as the most serious threat to public stability of any of the Christian-affiliated movements that have been growing rapidly as China undergoes a religious revival, she said.
"There have been reports of murders and beatings at the hands of the group, but also at a more general level, very aggressive proselytizing, harassment, brainwashing," said Dunn. "Those accusations are very routine."