"We have a lot of rumors and innuendos out there, but nothing has been founded yet," said Homicide Sgt. Bob Wilkins.
Police were led to Nicodemo, 41, when an SUV seen fleeing the scene was later found parked in front of his house on 17th Street near Hartranft, in Packer Park. A source said that a gun was found in the vehicle.
In addition to the arrest of Nicodemo, police still may be searching for more suspects.
The slaying happened just hours after federal prosecutors rested their case against reputed Mafia boss Joseph "Uncle Joe" Ligambi and six co-defendants in a mob racketeering trial.
Lawyers for the defendants were furious Thursday over the killing because it could sway the jury as the defense team prepares to make its case in the trial.
"I can't f------ believe this," said Joseph "Scoops" Licata's attorney, Christopher Warren, as he greeted the defendants Thursday morning before U.S. District Judge Eduardo Robreno entered the courtroom.
"We're preaching a theme of nonviolence, and three hours after the government rests, someone is shot in front of their house in broad daylight," Warren said. "What could be worse?"
Members of the defense team said that none of their clients was involved in the shooting, but they expressed concern that jurors - even though they are not supposed to follow media coverage of the case - could read about the arrest and the speculation that DiPietro's death is the city's first mob hit since John "Johnny Gongs" Casasanto was murdered in 2003.
"It's all over the Daily News," Warren told Robreno. "I think it would be naive to assume the jurors are not going to be exposed to this."
Robreno agreed to call each juror into his chambers when the trial resumes Tuesday morning and ask if they've seen any of the news coverage and, if so, whether they could disregard the information and render an impartial verdict.
Police would not confirm widespread rumors that DiPietro had been cooperating with law enforcement. However, in a 2008 federal indictment, prosecutors alleged that John Condo, a one-time co-conspirator of DiPietro's, had a conversation with an unidentified person in 2004 who told Condo not to have any more "drug-related dealings" with DiPietro because he was a target of an investigation and someone close to him was an informant.
DiPietro - also known as "Knucklehead," according to court documents - pleaded guilty in 1997 to conspiracy to distribute cocaine and methamphetamine and was ordered to serve eight years in prison, followed by eight years of parole.
In 2008, while still on parole, DiPietro was named in another federal indictment that accused him of conspiring with two others to distribute cocaine.
Ligambi, 73, and his associates went on trial in mid-October on racketeering charges that focus on gambling and other nonviolent crimes.
"This would be a ridiculous time for us to start being violent," Ligambi's attorney, Edwin Jacobs, said outside the courtroom Thursday. He said that Ligambi, jailed since his arrest in May 2011, was not involved in DiPietro's death.
The jury was not present Thursday, the phase of the trial when defense lawyers make long-shot arguments for acquittal on behalf of their clients. When Licata asked Jacobs about the chances that Robreno would throw out the case, Jacobs replied: "When's the last time you saw a pork chop at a bar mitzvah?"