The verdicts came at the end of a seven-day trial before Judge W. Craig Broadwater.
Turner and Sellers were found guilty of committing a killing in furtherance of a continuing criminal enterprise; criminal conspiracy to distribute crack cocaine; interstate travel in aid of a racketeering enterprise; and carrying and using a firearm in commission of a crime of violence.
Turner also was found guilty on a separate count of operating a continuing criminal enterprise.
Broadwater is expected to hear post-trial motions from the defense in early January. Assistant U.S. Attorney Robert McWilliams said he does not expect the two to be sentenced before February.
"I'd like to think it's cumulative. The fingerprint and blood evidence corroborated the testimony of the witnesses," McWilliams said after the verdicts.
A leather jacket owned by Turner had both his blood and that of Folmar on the inside of the right sleeve, according to testimony.
A fingerprint from Turner's left middle finger was found on the driver's side window of Folmar's car.
"There wasn't any physical evidence at all that tied him (Sellers) to it," said Harry Smith, the court-appointed attorney for Sellers. He said an appeal was "a good possibility."
Stephen Herndon, Turner's attorney, tried to persuade the jury that someone else could have been wearing the jacket when Folmar was killed. In his closing arguments, he said police had found no blood in the right-hand pocket of the jacket, although Turner had cut his right hand, and the gun used in the killing was stained with Folmar's blood.
During his closing argument, McWilliams took the jacket before the jurors, pulled out the lining of the pocket and showed them a nickel-sized brownish red spot. He told them the police had not done DNA testing on every bloodstain they found.
During the trial, several witnesses testified that people on Ray Street were yelling "cop" and "five-oh" when Folmar drove onto the street. Another said Folmar earlier in the day had witnessed Turner selling drugs.
"There's no other reason to kill this woman. Boo (Turner) was afraid she could rat him out. This was a hit," McWilliams told the jury.
McWilliams said more than an hour may have elapsed from the time Folmar was shot in the jaw and the two fatal shots were fired. She had also been stabbed 11 times.
According to testimony, several people saw that she was injured after the first shot, but never called police.
Witnesses, many of them convicted felons or testifying under grants of immunity, said Turner rode to the corner of Ray and East German streets on the back of Julian Pace's bicycle. Pace said he saw Turner fire the first shots.
Other witnesses said Sellers gave Turner the gun and later heard Turner ask him for a razor.
"I'll remember them in my prayers. I know they're hurting just like I am," said Folmar's mother, Ruby LaBelle, of Turner's and Sellers' parents. LaBelle and Jacquelin Turner both shed tears in the courtroom.
Turner's and Sellers' parents declined to answer questions.
"We had our doubts about the justice system, but we see justice has been done," said Folmar's brother, John Staubs of Harpers Ferry, W.Va.