"There are lots of people who want to see me die," he rapped in Spanish over an ominous melody, flashing a middle finger at the cellphone camera. "I'm not going anywhere."
Sosa Rivas uploaded the video — titled "I'm Still Alive" — to YouTube on Dec. 10, 2016.
Three weeks later, his mutilated body was dumped in the Potomac River.
Within days, members of his clique retaliated, torturing and murdering a 15-year-old girl who they believed had lured him to his death, authorities say. One of her killers pleaded guilty in court last week, where prosecutors played chilling videos of the crime.
The brutal, connected killings have drawn attention to the resurgence of MS-13 in the Washington area. The gang has been linked to more than two dozen homicides in the region over the past two years.
But the two cases have also cast a spotlight on Sosa Rivas's music and the role amateur rap videos have played in the gang's rise across the country.
MS-13 uses the videos to represent their cliques, intimidate rivals and recruit members, said Lt. Jonathan Weeks, commander of the Northern Virginia Regional Gang Task Force.
"These rap videos are a powerful tool, especially in the age of social media," he said.
Twice in the past six months, federal prosecutors in Maryland have cited rap songs in racketeering cases targeting the gang, saying the recordings "promote MS-13 and its activities."
Like narcocorridos , songs that recount the exploits of Mexican drug cartels, MS-13 raps mythologize the gang and create a sense of community among its members, according to those who study the phenomenon.
But gang members also listen to these songs during the commission of crimes, authorities say, like a soundtrack to MS-13 mayhem.
'Time to kill'
MS-13 was founded by Salvadoran refugees in Los Angeles in the 1980s, when West Coast rap was gaining fame. Gang members soon began making their own Spanish-language anthems in the style of N.W.A. and Cypress Hill. And when the Clinton administration deported thousands of MS-13 members to Central America in the mid-1990s, they brought the music with them, according to Alex Jacky, an academic who has studied MS-13 culture.
The gang's music videos began appearing a decade ago on YouTube, where some have been viewed millions of times. Although its style hasn't evolved much over time, the music allows MS-13 members to tell their stories, Jacky said.
"It provides a raw, open arena for them to express their lives in the way they best know how," he said. "You spit what you know."
The problem with spitting what you know on the Internet, however, is that other people then know it, too.
Like prosecutors in Maryland.
One of their two recent indictments names an alleged MS-13 rapper as Junior Noe Alvarado-Requeno, a.k.a. "Insolente."
There are at least 10 MS-13-related videos attributed to Insolente on YouTube, including several featuring "Largo" — the alias of a defendant in the other indictment.
One of the videos — uploaded in July, a few months before Alvarado-Requeno was charged — pays tribute to a fallen gang member nicknamed "Snaider," from Langley Park, Md. As the video cycles between photographs of MS-13, Insolente's lyrics alternate between sweet and chilling.
"Life has dealt us another blow. Another brother has been taken from our side," he says. "Remember a brother who was a criminal and very sincere. Who was always one of the first in line when it came time to kill."
The song ends with a warning to MS-13's enemies.
"Those wusses are going to pay for this," Insolente says. "When they least expect it, we're going to hit them back. In revenge for our fallen homeboy."
'See, Hear, Shut Up'
Sosa Rivas always seemed to have a cellphone at hand, ready to record. Calling himself "Cristian Jenner," he posted dozens of videos on YouTube and Facebook, where he challenged other rappers, asked for "likes" and accumulated followers. He posed for photos in a white silken jacket with "Team Jenner" on the back or shirtless to show off the words "Only God Can Judge" tattooed across his chest.
Despite MS-13's motto of "See, Hear, Shut Up," Sosa Rivas didn't hide his affiliation with the gang. Instead, he boasted about it.
"Respect the leader of the Harrison [clique]," he rapped in one video. He and his clique members posted photos of themselves making gang signs under MS-13 graffiti, and Sosa Rivas even dropped his street names "Sombra," or shadow, and "Black Boy" during songs.
It's unclear whether the videos played a role in his downfall. Prosecutors in Prince William County consider them "important evidence," a spokesman said, but wouldn't comment further. And a spokesman for county police said the detective handling the case was "aware of the videos but, to his knowledge, no song or lyric was directly related to [Sosa Rivas's] death." Both said such videos were not uncommon in gang cases.
Court records offer several explanations for the slaying, including MS-13 anger at Sosa Rivas for passing himself off as a gang leader and punishment for his allegedly hanging out with rivals, stealing from the gang or killing someone.
What is clear is that Sosa Rivas somehow crossed the Coronados and Via Satellite cliques. Their members then contacted MS-13 leaders in El Salvador, who "green lit" his killing, according to an FBI affidavit.
Two months before his death, Sosa Rivas's videos took a dark turn. In one titled "Forgive Me Mom," uploaded to YouTube on Nov. 9, 2016, he mused about his own death while playing with a handful of bullets.
"I can't believe they are going to bury me," he raps before telling his mother, "I would have liked for you to have been called 'grandma.' "
A month later, he was more defiant as he rapped from the back seat of the dimly lit car.
"I'm being followed, [gunshots] sounding all around me," he said. "I've built myself armor that my haters can't destroy."
But that armor failed him three weeks later, in the early hours of New Year's Day. Sosa Rivas had been lured to a park in Dumfries, Va., under the pretext of smoking marijuana with a girl he had once dated, according to authorities.
"Come sit with me," the unidentified woman texted Sosa Rivas, moments before four men from the two cliques attacked him with machetes, sticks and rocks, according to the affidavit. The men are accused of dragging him to the Potomac, where one of them stood on the body to submerge it before piling rocks on it.
Members of Sosa Rivas's clique blamed 15-year-old Damaris Reyes Rivas, who played a role in luring him to the park, though she may not have been there herself. They sought revenge before police could even find his body. On Jan. 8, they used a similar ploy to draw her to Lake Accotink Park in Springfield, where they forced her to strip in the freezing cold, tortured her and interrogated her about Sosa Rivas's death.
When Damaris admitted she had slept with Sosa Rivas, his girlfriend, Venus Romero Iraheta, then 17, told her she'd see her in "f---ing hell" and plunged a large hunting knife into her, prosecutors said in court. Iraheta also sliced off the dollar-sign tattoo Sosa Rivas had given Damaris.
It was more than a month before authorities found Damaris's body.
At least 18 teens or young adults have been arrested in connection to the two killings.
On Jan. 8, Iraheta pleaded guilty in Fairfax County Circuit Court to abduction and murder. Before playing videos the gang took of Damaris's torture, Commonwealth's Attorney Raymond F. Morrogh described how Iraheta and her clique had packed inside a green Nissan Armada with their victim.
As they drove the frightened 15-year-old to her death, he said, they listened to "MS-13 music."
Justin Jouvenal contributed to this report.