Only later, on Friday evening, did Xinhua provide more detail, confirming the Chengdu paper’s account. In a five-sentence report, it said the police, working for 33 hours, had solved the case. Mr. Yang, who worked in Kunming, had returned home and asked his parents for money. He had an argument with them and killed them on Wednesday evening, Xinhua reported. Later, in an effort to conceal his crime, he killed 17 other people. On Thursday, after being arrested in Kunming, he confessed.

The list of the victims reported by The Beijing News included three people surnamed Yang who all also had the character “qing,” which means clean or pure, in their names, suggesting that they might have been related. In all, 10 of the victims were surnamed Yang.

Interviews with residents of the area appeared to corroborate these reports. In Daibu Township, a sprawling mountainous locale that encompasses Yema, the killings were the main topic of conversation at the markets, residents said. One, a hotel owner surnamed He, said that at first people suspected the crime was a terrorist attack, echoing the killings in Kunming in 2014 by militants from Xinjiang that left 29 people dead.

Then, people learned that the suspect in the killing was from the area, socially awkward and liked to gamble, Mr. He said, adding that most of the dead were relatives of Mr. Yang.

Another resident, a woman surnamed Li, said that the tiny hamlet within Yema where the killings took place, called Baifengwan, was particularly remote, and that many people had never heard of it.

At midday on Friday, the home page of the official news portal in Kunming focused on a story about the local real estate market. The train crash in Hoboken, N.J., received extensive coverage nationwide, as did the override of President Obama’s veto of the Sept. 11 victims’ bill, which was a “hot topic” on Weibo, China’s Twitter-like social media platform. The Yema killings were not.

“Nineteen people died, and CCTV doesn’t have a report on it,” wrote one Weibo user called “Starry Sky in a Sunny Room,” referring to the state television network. “Speechless. Chinese news is villainous.”