The Uvalde shooter threatened girls on social media and vowed to shoot up a school there, he was reported but nobody took him seriously until it was far too late.
Three users said they witnessed Ramos threaten to commit sexual violence or carry out school shootings on Yubo, an app that is used by tens of millions of young people around the world.
The users all said they reported Ramos' account to Yubo over the threats. But it appeared, they said, that Ramos was able to maintain a presence on the platform. CNN reviewed one Yubo direct message in which Ramos allegedly sent a user the $2,000 receipt for his online gun purchase from a Georgia-based firearm manufacturer.
"Guns are boring," the user responded. "No," Ramos apparently replied.
In a statement to CNN, a Yubo spokesperson said "we are deeply saddened by this unspeakable loss and are fully cooperating with law enforcement on their investigation."
Yubo takes user safety seriously and is "investigating an account that has since been banned from the platform," the spokesperson said, but declined to release any specific information about Ramos' account.
Use of Yubo skyrocketed during the coronavirus pandemic, as teens trapped indoors turned to the app for a semblance of in-person interactions. The company says it has 60 million users around the world -- 99% of whom are 25 and younger -- and has trumpeted safety features including "second-by-second" monitoring of livestreams using artificial intelligence and human moderators.
Despite those safety features, the users who spoke to CNN said Ramos made personal and graphic threats. During one livestream, Amanda Robbins, 19, said Ramos verbally threatened to break down her door and rape and murder her after she rebuffed his sexual advances. She said she witnessed Ramos threaten other girls with similar "acts of sexual assault and violence."
Robbins, who said she lives in California and only ever interacted with Ramos online, told CNN she reported him to Yubo several times and blocked his account, but continued seeing him in livestreams making lewd comments.
"[Yubo] said if you see any behavior that's not okay, they said to report it. But they've done nothing," Robbins said. "That kid was allowed to be online and say this."
Robbins and other users said they didn't take Ramos' comments seriously because troll-like behavior was commonplace on Yubo.