Traci Miller, an assistant commonwealth’s attorney, has experienced the shift firsthand in the more than a decade that she has been with the office.

“Everybody has a gun at their disposal, and so things that might have been settled with a fistfight back in the good old days are now settled at the end of a gun,” Miller said.

Guns are stolen, or purchased by people with clean records and given to young men, sometimes by their own mothers, Miller said.

“Just as quickly as the police can get the gun off the street, they can make a phone call and get another gun,” she said.

Often, prosecutors do not even try to give a motive for murder, she said; the gravity of the crime juxtaposed with the triviality of the motive is simply too jarring.

“It’s so senseless that I don’t want to try to sell that to a jury,” she said.

Prosecutors have stopped asking that judges tell jurors that they do not have to prove motive to prove their case, said Deputy Commonwealth’s Attorney Learned Barry, who helps oversee most homicide prosecutions in the city.