For more than a year, authorities believe, Steven "J.R." Blackwell Jr. was at the center of a street war with a rival faction that saw as many as two dozen people shot across Baltimore.

In an empty federal courtroom Wednesday, the 27-year-old Blackwell, never previously convicted of a crime, pleaded guilty to overseeing a multimillion-dollar heroin conspiracy and laundering the proceeds through gambling winnings in Las Vegas and state lottery tickets.

Though the charges were devoid of accusations of violence, court records have linked Blackwell to a wave of shootings and killings touched off by the April 2008 abduction of his then-teenage brothers. Blackwell's plea agreement, which came days before he was to have gone to trial, calls for him to serve 20 years in prison in a case in which he faced life.

"This case will be recorded in the books as a drug and tax prosecution, but it is an example of how we use federal law enforcement resources to fight violent crime," U.S. Attorney Rod J. Rosenstein said in a statement. "Drug dealers whose criminal enterprises spawn violence are at the top of our list."

Much of the Baltimore's persistent violence is related to the drug trade, but the brazenness of the tit-for-tat bloodshed that authorities believe was associated with the feud between Blackwell and the rival Chapel Hill Boys was particularly shocking: a fatal ambush at a family appliance store a shooting outside a funeral, and the spraying of gunfire at a backyard cookout that wounded 12 people.

Federal law enforcement agencies including the FBI, Drug Enforcement Administration and Internal Revenue Service spent years with city police and prosecutors building a case that eventually focused on drug-dealing and money-laundering. In August 2010, Blackwell, his girlfriend, Joy Edison, and a courier named Tahirah Carter were indicted by a federal grand jury.

"I don't know anything about violence — that was not alleged in this case," Blackwell's attorney, Harry Trainor, said Wednesday. Of the guilty plea, Trainor said: "He's been willing to plead in this case since the first time we met — it's been a matter of working out the terms."

Blackwell, clad in a burgundy jumpsuit, smiled as he was led into the courtroom. He sat down at the defense table, turned around and with a smile shrugged at a DEA agent who had arrested him in the Bronx, N.Y., last year. U.S. District Judge Catherine C. Blake read from Blackwell's plea agreement, and he nodded along with a monotone "Yes, ma'am" as she asked if he understood its terms.

Prosecutors are seeking to seize $10 million from Blackwell, and he has agreed to forfeit eight properties: seven dilapidated homes from around Baltimore — Trainor said the homes were not drug stash houses but rehab projects — and his Elkton residence, which was purchased for $740,000.

As part of his plea, he admitted purchasing heroin from a New York supplier and selling it in "shops" in the Pimlico area of Northwest Baltimore and Patterson Park Avenue on the east side, among other places. To launder the proceeds, he gambled drug proceeds at the Venetian, Caesar's Palace and the MGM Grand in Las Vegas, and purchased "winning" lottery tickets in excess of $138,000 to disguise his income as legitimate lottery winnings, according to records.

Blackwell's downfall traces back to a dispute with a former business partner, officials say.

Federal agents wrote in court papers two years ago that Terrell Allen, the head of a drug ring referred to as the Rich-Allen Organization or Chapel Hill Boys, was receiving heroin from Blackwell. But the two fell out because Allen believed Blackwell was cheating on the weight of the drugs while raising the price, the records show.

On April 25, 2008, authorities said in court papers, Allen, Omar Spriggs, and Demetrious Rich were among six masked gunmen who forced their way into a Catonsville home, bound and gagged 10 occupants with duct tape, and held them at gunpoint from 3 a.m. until 11 a.m. One woman reported being sexually assaulted.

(Allen's attorney, Gerald Ruter, in 2009 "categorically denied" that Allen was involved and said the police information was "invented.")

Blackwell arrived at the home as the kidnappers were fleeing in a Chevy Suburban with his two brothers and was shot at but not hit, police said. The abduction prompted an Amber Alert for the brothers, Stephon and Sterling, but was quietly resolved without criminal charges.

A source told federal agents that Blackwell paid $500,000 for his brothers' release, and they were returned three days later without incident.

Six weeks later, agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives wrote in court papers, gunmen took revenge with a quadruple shooting outside the Allen & Family Appliance store, a mom-and-pop business that sells discount appliances in East Baltimore. Spriggs and Allen's father, Tony Allen, 52, was killed, and Terrell Allen was injured.

As many as 27 people may have been shot in the violence that ensued in those 15 months, according to court documents and sources, most of it targeted at Blackwell's associates.

Anthony Izzard, 25, was killed in a triple shooting in the 1700 block of W. Lexington St., which authorities believed was related to the kidnapping. Then at Izzard's funeral, gunman shot two people, killing Michael Ellerby, 24. Three months later, Quinton Hogan, 23, Donell Rogers, 21, and Troy Wilson, 17, all believed to have been Blackwell associates, were killed.

In February 2009, 26-year-old Eric Pendergrass was abducted and held for ransom, and later found dead, floating in the Patapsco River. Police believed he had connections to the Blackwell family, sources said at the time.