"He's a criminal and a bad cop, but he's not a drug dealer," Valvo said, adding that Williams never had the "specific intent" to possess or deliver drugs.
Authorities said Williams, 27, and two other then-officers, Mark Venziale, 32, and Robert Snyder, 30, hatched a plan last May with drug dealer Angel Ortiz to steal the heroin from a supplier, then share the profit when it was sold.
Venziale, who testified against Williams, and Snyder both pleaded guilty last month to drug conspiracy and related offenses, and are to be sentenced in May.
Prosecutors said Williams and Venziale were in uniform in their cruiser when they conducted a sham traffic stop of Ortiz on May 14 and pretended to arrest him. Ortiz had just received a heroin delivery from a courier who witnessed the car stop.
The men released Ortiz, who had given the drugs to a man they believed was a drug dealer and money launderer - an undercover Drug Enforcement Administration agent who had infiltrated the plot and had said he would sell the heroin later that day in Camden and then share the profit.
The two cops later split $6,000 in cash they got for the heist, Venziale testified.
Valvo told the jury that Williams engaged in nothing more than a "car-stop for hire."
Assistant U.S. Attorney Anthony Wzorek scoffed at the claim, saying that Williams "knew exactly" where the money was coming from.
Authorities said Ortiz, who also pleaded guilty in the case last month, was an associate of convicted murderer and reputed drug dealer Zachary Young, who has pleaded not guilty.
Young's attorney, Anna Durbin, accused prosecutors of "scraping the bottom of the barrel" by targeting Young, whom she described as "a sick, old man." Young, who has diabetes and has lost a foot, sat at the defense table in a wheelchair.
Durbin said that Ortiz was the big-time drug dealer and that Young was simply "a lot of hot air," referring to Young's voice on wiretaps. He said Young never had any drugs, money or people working for him.
Williams and Snyder were also accused of planning to steal cash on July 9 from a man Williams believed was a bookie with mob ties. That scheme also involved a phony car-stop, but the feds aborted that robbery.
During the trial, prosecutors played audiotapes of incriminating conversations between Ortiz and Williams as they discussed the drug heist, portions of which were replayed for the jury yesterday.
The jury deliberated for an hour yesterday without reaching a verdict, Wzorek said.