"You're asking me not to let them out," Lerner said. "You're asking me to treat them the same way that the court treated their relatives who actually committed the murders."
Coulter sobbed: "This is never going to end. They're not going to stop. They never will."
Merlo, 48, and McDowell, 26, pleaded guilty to threatening Coulter and Amanda Brannan - two prosecution witnesses at the 2010 trial of Gerald Drummond, 28, and Robert McDowell, 29.
Drummond and Robert McDowell were both found guilty and sentenced to life in prison without parole in the racially tinged slayings of Damien Holloway, 27, and Timothy Clark, 15. The victims were forced to kneel and then shot execution-style on a Tacony street July 13, 2007.
Merlo is Robert McDowell's mother. Tara McDowell is Drummond's sister and has two children from her relationship with Robert McDowell.
Assistant District Attorney Carlos Vega asked Lerner to sentence the women to three to six years each - citing the threats that have marked the case since 2007.
But Lerner said that because the women had no criminal records and pleaded guilty, a long sentence would be reversed on appeal.
Lerner sentenced Merlo to seven to 23 months in prison followed by four years of probation; Tara McDowell got time served and four years of probation.
Lerner also ordered the women, their relatives, and friends to stay away from Coulter and Brannan: "If there is so much as a peep out of either of you, or anybody else acting on your behalf - related or not - your sentence will be measured in years rather than months."
Lerner noted that there was an ongoing investigation of threats against witnesses allegedly made by other Drummond and McDowell relatives.
Merlo said nothing before sentencing; her lawyer, Joseph J. Valvo, said she feared she would hurt her case.
Tara McDowell apologized for the threats and told Lerner, "I've learned my lesson. . . . It won't happen again."
She said she wanted to be reunited with her son, 7, and daughter, 4, and move away from Philadelphia.
Witness intimidation and threats were a constant in the investigation of the double murder, through the trial, and afterward.
The two women were charged after a chance Nov. 1 confrontation in a doctor's office, where they threatened Coulter and Brannan, saying they and their children would be killed and that "there was a contract on them."
The scene was so loud that the doctor's staff called police.
At trial, witnesses said Holloway, who was African American, was killed because he was disrespectful to Drummond's sister, with whom he had a child. Clark, who was white, was Holloway's friend and helper in a lawn-cutting business and was killed because he was there.
Threats and violence in the neighborhood were so pervasive it took more than a year before police arrested Drummond and McDowell. At trial, another Merlo son was arrested after allegedly threatening Brannan in a hall in the Criminal Justice Center.
Lerner said witness intimidation and retaliation had become so commonplace it "damages the justice system . . . and poisons every single neighborhood from which these cases arise."
Contact Joseph A. Slobodzian at 215-854-2985 or firstname.lastname@example.org, or follow on Twitter @joeslobo.