"A massive murder occurred in Zhaike Village, Luohe Town, Rizhao Ju County, Shandong Province. News of the incident was blocked by the authorities, and relevant reports and online information were deleted and blocked. However, news gradually spread overseas, indicating that the murderer was a local villager in his 10s......The more reliable news is that the murderer is in his thirties, has a slight disability, and was adopted to his uncle since he was a child.
The murder occurred in the middle of the night (that is, in the early morning of the first day of the Lunar New Year). When the villagers found out, they first called the 120 emergency hotline. Medical staff Arrive at the scene before the police. A medical worker was eager to save people, but the murderer squatted at the scene and made a surprise attack, causing him to be attacked and killed.
A netizen who claimed to be from Ju County said: The murderer was a migrant worker. He was abused by his stepfather at home and bullied by his teacher in school. During the Chinese New Year, he went home and shot his teacher and his whole family with a nail gun he modified.
Then went home and took a nap.
Around seven o'clock, they went out again and shot them from house to house. People who were celebrating the New Year were all watching TV at home and no one came to visit, so they didn’t notice it. The sound of firecrackers outside covered up the sound of gunfire. We visited five houses in total, 14 people died and 5 were seriously injured."
The account you posted seems to make sense as to how he could do it.