The attack on May 5, 2017, came at a moment when MS-13's ranks in the jail were at an all-time high — the result of a nationwide crackdown on the violent street gang. Of the jail's 900 or so inmates at the time, officials said, about 50 were tied to MS-13.
"Our incidents every month are predominantly MS," said a Prince George's jail investigator, speaking on the condition of anonymity for his safety. "They are vying for control of these housing units."
As bodies bearing MS-13's trademark stab wounds and machete slashes have appeared in quiet suburbs and secluded parks across the country, authorities have increasingly gone after the gang. From New York to Virginia to Texas, they have arrested hundreds of members of MS-13 over the past two years.
But that effort is now posing its own problems.
As jails fill with MS-13 members, facilities are feeling the strain. Fights are up. So is extortion. And jailers are struggling to keep MS-13 members away from one another and their rivals.
"MS-13 presents unique challenges not only to the criminal justice system but also to the correctional system," said Robert Green, head of corrections in Montgomery County, where the gang has been linked to nearly a dozen killings since 2015.
"Gang altercations have significantly increased" over the past year, he said, as the jail's MS-13 population has risen 20 percent.
On Long Island, where a string of MS-13 killings has been invoked repeatedly by President Trump, the gang's jailhouse ranks are also up 20 percent compared with two years ago, Suffolk County officials said.
In Prince William County, Va., MS-13 jail membership is up 32 percent over the same time period.
And in neighboring Fairfax County, the gang's jailhouse ranks have doubled in the past year, leading to what officials call a "turf war" between MS-13 and a coalition of other gangs.
Organized crime is nothing new inside the U.S. correctional system: The Bloods, Crips, Latin Kings, Aryan Brotherhood, Mexican Mafia and Black Guerrilla Family have long held sway in jails and prisons across the country.
While jail officials acknowledge that the recent influx of MS-13 inmates has made their jobs harder, they also emphasize that the gang is just one of many within their walls and that the situation is under control.
Nonetheless, the rising number of MS-13 members in the United States' jails reflects both the gang's resurgence and law enforcement's renewed efforts to combat it.
"We have sent thousands and thousands and thousands of MS-13 — horrible people — out of this country or into our prisons," Trump said during his State of the Union address as the parents of two girls killed by the gang in Long Island watched and wept from the balcony.
'They're going to fight'
Officers at the Prince George's jail began to notice a rise in MS-13 five years ago. As the gang gained strength, it began to flex its muscle by demanding a "tax" from other inmates, particularly Hispanic convicts. Promising them protection, MS-13 members took a share of their commissary, including chips, candy, T-shirts and boxer shorts.
"They control the Hispanic population," the investigator said. "They make them pay rent like they do on the streets. They make them work out. They make them join with them in fights."
By the spring of 2016, however, inmates in two of the jail's 18 housing units had grown tired of the extortion, the official said. Whenever an MS-13 member was transferred into those units, other inmates would immediately attack him.
"When it happened two or three times in one month in the same unit, that's when we figured out what was going on," he recalled. "They said they couldn't take it anymore."
A similar revolt is underway in the Fairfax County jail, where MS-13 has grown from less than 20 members a year ago to about 40 today. In response to that rise, a few dozen of the jail's 1,000 inmates have rallied behind another gang, the 43 Mob, for protection.
Extortion by both gangs has gone up, according to Georgi Hovhannisyan, commander of the Sheriff's Intelligence Unit at the jail. And gang fights that used to occur roughly twice a year are now monthly affairs, he said.
Unlike state and federal prison systems, where inmates are often sent to far-flung facilities to serve lengthy sentences, county jails are designed to hold defendants as they await their trials. Many counties only have one jail, and it's often attached to the courthouse.
These limitations have left jails scrambling to deal with the MS-13 influx.
Adding to the challenge is the sheer size of many MS-13 cases.
"It seems like the days of one person committing one crime is gone," said Green, the corrections chief in Montgomery, adding that cases with a half-dozen co-defendants are now common. "That requires us to keep those people separate as best we can."
Compounding the problem is the high percentage of MS-13 cases that are slayings, in which bail is unlikely and proceedings move more slowly than they do for less serious crimes.
"We're not going to deal with those guys for a day, a week or even a month," said a Montgomery jails investigator, speaking on the condition of anonymity to maintain his safety. "We're dealing with them for a year, a year and a half."
In addition to keeping co-defendants apart, jails also have to separate MS-13 members from their rivals, particularly those belonging to bitter enemy the 18th Street gang.
"MS-13 and 18th Street gang have something called a J.O.S., or 'jump on sight' order," Green said. "If they come in contact with each other, they're going to fight."
Some skirmishes are personal, like last year when an 18th Street member ended up in the Prince George's jail at the same time as the MS-13 shooter who'd targeted him.
This complex web of cases, grudges and rivalries requires officials to quickly determine which inmate belongs to which gang. Sometimes officials know an inmate's affiliation ahead of time thanks to police or criminal records. But identifying gang members has grown more difficult as MS-13 has moved away from the tattoos for which it was once known.
Many jails conduct sporadic shakedowns, scouring cells for signs of gang affiliation, such as clique acronyms in gothic lettering or devil horns drawn on the wall.
"We're seeing a lot more graffiti," said Hovhannisyan. "It's their way of letting everyone know 'We're here.' "
In the Prince George's jail, investigators' office walls are lined with confiscated MS-13 drawings of women in clown paint, skulls wearing fedoras and demons dancing in hellfire. Sometimes gang members subtly try to escape their censors, as when one MS-13 member drew a clock with its hands at 1 and 3.
Officials occasionally discover coded letters during shakedowns, which they send to the FBI to be deciphered. Evidence of gang ties isn't just useful for keeping rivals apart. It can also be used against gang members in court.
When particular MS-13 members prove too problematic, or when one snitches, officials will sometimes trade them with another jail.
Prince William's jail was already at capacity before the recent MS-13 influx. Now that 4 percent of the jail's population — or about 40 inmates — are allegedly MS-13, officials are increasingly having to swap gang members with neighboring jails, like a juggler with ever more balls in the air.
"It's very logistically challenging," Maj. Mandy Lambert said with a sigh.
'I'm not in a gang'
When a reporter for The Washington Post visited the Prince George's jail in November, the number of alleged MS-13 members had dipped to 23, including one woman. More than half had been charged with murder, and at least four others were accused of attempted killings.
Small signs of the gang's influence were everywhere, from the names of cliques carved into the beige paint to the soccer goals drawn in soap on the basketball court to the nightly Spanish TV shows that stirred the ire of non-Hispanic inmates, especially during sports playoffs.
"The non-MS Hispanic guys will join in with MS for that because they want their right to watch TV," the investigator said.
Among the MS-13 members left at the jail were the two accused of attacking the Blood in May. Marvin Vazquez-Juarez, 20, had been locked up for killing his girlfriend, whose body was discovered in a Hyattsville park on New Year's Day 2016. He would later be convicted. Julio Lopez-Gomez, 26, had been charged with multiple assaults and robberies.
The attack sent their victim to the hospital and led to attempted murder charges.
Four alleged MS-13 members agreed to be interviewed by The Post, emerging one by one from a labyrinth of locked doors and whitewashed halls to sit at a table in a tiny room, where guards removed their handcuffs.
"I know gang members, but I'm not in a gang," said Angel Flores-Aguilar, a 20-year-old Honduran accused of shooting a gang rival as his friends listened over the phone. He wore a bright yellow jumpsuit signaling disciplinary problems. "The police think every Hispanic is a gangster."
"I don't know why I'm here," said a baby-faced Guatemalan who'd recently turned 18 behind bars. He had dreamed of being an algebra teacher or playing soccer for FC Barcelona. But prosecutors said he'd fatally shot an 18th Street member. A jury agreed.
"It is what it is," he said of the life sentence he had received two weeks earlier. He and two others agreed to speak on the condition of anonymity.
A 19-year-old from El Salvador admitted falling in with MS-13. It began when he met some kids playing soccer in the park, he said. Soon he was skipping school with them to smoke marijuana.
"They had girls and parties," he said. "I wanted to know what it was like."
He'd only hung out with hard-core members for a month, he said, when his new friends fatally attacked two rivals with knives and a baseball bat. He claimed he didn't participate but nonetheless pleaded guilty to first-degree murder.
"Now I regret joining them," he said.
"Le da paja a uno," he added in Spanish. "They feed you lies."
An older inmate with MS-13 tattoos said he'd joined the gang as a teen in El Salvador to avenge his grandfather, who'd been killed by a machete-wielding robber. He'd then come to the United States in 2000. When he was deported in 2012, he came back a few years later to be with his wife and children.
"I don't kill nobody in the United States," he said in English.
Asked whether he could say the same about El Salvador, he laughed.
"You know my answer," he said before shuffling down the long white corridor toward his cell.