They stabbed him eight times, blindfolded him with duct tape, weighed him down with a bucket of cement, then threw him into the Schuylkill. And still, Tan Voong survived to clamber out of the inky waters, flag down a passing car, and eventually identify one of his would-be killers.

His testimony helped put Tam Minh Le, a reputed Vietnamese gang member in South Philadelphia, on death row for the murders of Viet and Vu “Kevin” Huynh, brothers also left to drown that August night in 2014. But the identities of the masked men who Voong said had helped Le abduct, torture, and kill his victims remained unknown.

Now, nearly six years after Voong’s remarkable river escape, federal authorities have quietly charged six other suspects who they say either enlisted Le or helped him carry out one of the city’s most vicious incidents of gang violence.

In indictments unsealed as recently as this month, the six defendants range from a 48-year-old dim sum restaurant employee from Queens, once reputed to have been the fourth-highest-ranking member of a gang that terrorized New York City’s Chinatown in the 1990s, to a man who has confessed to helping Le escape Philadelphia as the dragnet tightened around him.

Newly released court records and interviews with U.S. Attorney William M. McSwain, prosecutors in his office and FBI investigators reveal a broad account of the night the Huynh brothers died — a story that spans several states and has its roots in the aftermath of the Vietnam War.

“The hope is that these men won’t ever have the opportunity to do something like this again,” said Scott Baber, a member of the team of Philadelphia-based FBI agents whose efforts led to the arrests. “Until they were charged, we had people out on the streets who had quite literally gotten away with murder.”

‘Where is the money?’

The testimony that Voong, 24, offered at Le’s 2016 trial provided a starting point for an investigation that would last more than two years.

He told jurors that his friends the Huynh brothers — whom authorities had long known as South Philadelphia marijuana dealers — sought his help on Aug. 26, 2014, to raise money for a $300,000 drug debt they owed their supplier in California.

Voong scraped together what he could. But when he showed up as directed at Le’s house on 72nd Street in Eastwick with only $41,000, things quickly went south.

Spotting the Huynhs tied up in Le’s garage and stripped to their underwear under the watch of masked gunmen, Voong turned and tried to flee, only to be pistol-whipped, stripped, and zip-tied like the others.

“They kept saying, ‘Where is the money?’” he later told jurors. When his answers failed to satisfy, Voong testified, Le and his accomplices loaded their captives into a van and drove them to the river.

Le was familiar to Voong. The Huynhs had previously introduced him to the man as their “god-brother.” But when FBI agents interviewed Voong after his escape, he couldn’t identify any of the masked men.

Mike Breslin, supervisor of the FBI’s Organized Crime Task Force in Philadelphia, said that in tracking down those assailants years later, Le’s cellphone records from that night, which largely traced back to anonymous burner phones, were the only thing agents initially had to go on.

“This was the reverse of almost every other case that I’ve been involved in,” he said. “Usually, you have a cooperator and you confirm what they tell you with [cellphone] records. Here we were starting only with records and without any witnesses.”

An FBI team of agents and analysts that included Baber, Mike Fischer, Elizabeth DeAngelo, and John Kardos persisted for years, zeroing in on the few calls that traced back to registered accounts. They knocked on doors in Philadelphia and New York City, all the while trying to persuade the people behind them to help sketch out the network of those who knew of or were involved in the brutal events of that night.

“There were language barriers and cultural barriers,” Fischer said. “But as a group, I think they understood that these guys were bad and were willing to share as much information as they had.”

Assistant U.S. Attorney Robert Livermore, the prosecutor overseeing the case, had his doubts.

“When you’ve been doing this for a year and you still haven’t been able to identify anyone, doubt starts creeping into your mind,” Livermore said. “I was certainly willing to throw in the towel long before [the agents] were.”

But eventually, the trail led them to Lam Trieu, a 48-year-old restaurant worker from Queens who shared a striking link with Le: Both had been ranking members of a gang of Vietnamese immigrants that named itself “Born to Kill.”

Born to Kill

Taking their name from a slogan painted on helmets of some U.S. soldiers during the Vietnam War, “Born to Kill” members earned a reputation in the ‘80s and ‘90s as much for their spiked hair, sharp suits, and dark sunglasses as for their penchant for violence.

Based along Canal Street in Manhattan’s Chinatown, the gang largely recruited Vietnamese immigrants who, as children, had fled the political strife spawned by the war only to turn their aggression on Chinese and other Asian business owners in their adopted home city. They robbed rival gangs, ran protection rackets, and left a string of bodies across New York and North Jersey.

The FBI identified Trieu as one of the gang’s top leaders in a 1993 indictment that sent most of its upper echelon to prison and has since been credited with breaking “Born to Kill’s” back.

He was ordered deported after his release from prison, but as with many of the gang’s members, Vietnam refused to take him back. With nowhere to send them, the U.S. released Trieu and Le — who faced a similar deportation order after his own prison stint for a 1993 pool-hall slaying in Rochester, N.Y. — on immigration parole.

Trieu settled into a seemingly quiet life with his wife, children, and a restaurant job in Queens.

But federal authorities now believe that his old gang ties led to his involvement in the Huynh brothers’ deaths.

“If you’d asked me before this case whether BTK still existed, I’m not sure I would have said yes,” Breslin said. “I’m still not sure I’d say yes. But definitely, Tam Le and Lam Trieu’s prior involvement in BTK was a driving force in this.”

A remarkable escape

According to court filings submitted as part of the government’s investigation, the Huynh brothers’ supplier in California, whom authorities declined to identify and have not charged, deputized Trieu to collect on the $300,000 he was owed.

Traveling to Philadelphia with three associates, Trieu allegedly made contact with Le and issued orders for the brothers to be kidnapped and, if necessary, returned to New York as hostages. But as Trieu returned home, leaving his men — whom the FBI has identified as John Dao, 42; Jason Rivera, 34; and Trung Lu, 39 — to assist Le, the plan quickly went awry.

When Voong showed up with only $41,000, Le decided to have all three men killed.

Prosecutors now believe that Le — along with Trieu’s three masked associates and a fifth man, Minh Nguyen, whom Le had stationed outside his house as a lookout — bundled the Huynhs and Voong into a van and drove them to the grandstands along Boathouse Row.

“I felt sand on my feet,” Voong would testify later. “That’s when they started stabbing.”

Vu Huynh was stabbed 32 times, his brother an additional 28. Their throats were slit and, chained to cement buckets, both were thrown with Voong into the river alive.

Voong, who sustained stab wounds to his chest, back, and neck, recalled hearing the splash as the Huynhs hit the water and their anguished cries as they slowly drowned. He managed to make his way to a concrete wall lining the riverbank and clung to it to keep his head above water. Eventually, its rough surface helped tear the duct tape from his eyes, and over two to three hours he wriggled free from his bindings and climbed out.

When Philadelphia police asked Voong later that night who was responsible, he replied: “Lam [Trieu].”

Brought to justice

Dao, Rivera, and Lu returned to New York in the hours that followed. Investigators say Trieu was furious when he learned what had happened: Dead drug dealers don’t pay debts.

He allegedly sent the men back to Philadelphia to track down Voong and kill him before he could testify at Le’s trial. Those efforts failed, and Le was sentenced to death in December 2016.

Agents arrested Trieu in New York two years later as he was taking his children to school. He has pleaded not guilty to charges including conspiracy, extortion, and drug and racketeering offenses. He faces trial in June.

The three alleged masked men, Dao, Rivera, and Lu, also have been charged along with Nguyen, whom Le posted as the lookout outside his home that bloody August night. A sixth man, Hai Nguyen, 37, pleaded guilty earlier this month to lying to FBI agents about helping Le escape Philadelphia to upstate New York in 2014. It would be months before U.S. Marshals tracked down Le to Ashland, Va., in a Motel 6 where they caught him trying to escape through a bathroom ceiling.

Le is now on death row. All have been arrested except for Lu, who the FBI believes fled to Vietnam. The bureau is offering $10,000 for information leading to his arrest.