Police arrested Billy Xiong in December 2019 on suspicion of mail theft.
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That's when they say they found a Glock pistol connected to a mass shooting that killed four people, and started to build a stronger case against the suspects.
Before that, a series of stunned witnesses to the 2019 killings told Fresno police they couldn't see who did it and had no idea why anyone would've targeted their backyard football watching party.
A fun November day watching football with friends took a nightmarish turn when a group of gunmen appeared from the darkness and opened fire in an east central Fresno backyard.
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Most witnesses told police similar stories about their limited views.
"He saw two separate sets of muzzle flashes, but no figures, no bodies, and no face," said Sgt. Melanie Mayo of one of the witnesses she interviewed.
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Four people died and ten more suffered injuries.
Billy Xiong, Porge Kue, Ger Lee, and Anthony Montes are now facing charges of murder and more.
Police say they were gang members trying to get revenge for the murder of Randy Xiong earlier the same day.
But investigators say only one person who attended the party -- one of the four people killed -- might've had an affiliation with the rival gang.
"There were rumors that when he was younger, he used to hang out with a gang," Sgt. Mayo said witnesses told her about the man.
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Sgt. Mayo interviewed several of the attack's survivors.
RELATED: 4 men accused in deadly mass shooting in Fresno back in court
None of them seemed to know why they were targeted.
"They had no knowledge of any gang issues or personal issues that would have caused people to shoot all their friends and family," Sgt. Mayo said.
The preliminary hearing is expected to wrap up by the end of this week and then the judge will decide whether there's enough evidence for the four suspects to stand trial.