Others were more direct:
"I don't know why any prosecutor would drop a case like that," said L. George Parry, a former federal and city prosecutor now in private defense practice.
"It looks like there could be an entrapment issue," said Philadelphia litigator and defense lawyer Louis F. D'Onofrio.
On Monday, the day after The Inquirer published a lengthy article on the case, Kane defended her decision to abandon the investigation, saying it had been so badly mishandled by her predecessors that it could not be prosecuted.
She said the sting was tainted by racism, aimed almost solely at African American officials, and by an undercover operative, lobbyist Tyron B. Ali, whose credibility had been compromised.
After Ali taped the lawmakers and judge accepting money or gifts, more than 2,000 charges against him in an unrelated fraud case were dropped by the sting's lead prosecutor, Frank G. Fina, now head of the Philadelphia District Attorney's public-corruption unit, Kane said.
Ali was facing charges of stealing more than $430,000 meant for poor children and seniors when he agreed to cooperate with prosecutors in the sting.
People close to the investigation say they believe Kane killed a solid investigation against fellow Democrats.
Philadelphia defense lawyer Daniel McElhatton, a former assistant city district attorney, said prosecutors always face two key decisions during investigations: whether to file charges, and, if the answer to that is yes, how to try the case.
"The A.G. made a decision for whatever reasons that she was not going to let it get to the level [where] they were charged. Frankly I don't understand why," he said. "Those things that are impediments are things that defense lawyers could raise. But that's for a judge or jury to decide. . . . What you have is the A.G. making all the decisions that basically a trial judge might make."
An entrapment claim might or might not be valid, he said, but "it's usually the defense that goes through that. It's usually not the prosecution that says, 'We're not going to prosecute.' "
Sting-based prosecutions are particularly contentious.
Perhaps the most famous in history was Abscam, which unfolded in Philadelphia nearly 40 years ago, when an FBI undercover operation put six U.S. representatives and one senator in prison for bribery and conspiracy. Three Philadelphia city councilmen, including Council President George X. Schwartz, were also convicted in the case.
In Abscam, the FBI videotaped public officials taking money from fictional Middle East sheikhs. But not everyone captured on tape was charged with a crime.
As a tactic, stings have been controversial.
Critics say that when informants go undercover wearing a recording wire, prosecutors gain an almost unfettered ability to target suspects. Unlike taps placed on telephones, body wires require no advance approval by a judge.
As far back as 1928, Supreme Court Justice Louis Brandeis wrote, in a dissent, that the government "may not provoke or create a crime and then punish the criminal."
At the same time, defendants face a high bar in proving they were entrapped, that the government lured an otherwise innocent person into committing a crime. The modern legal standard requires defendants to show that the prosecution's conduct was "outrageous."
"You have to show the government really used strong-arm methods," said Bennett L. Gershman, a professor at Pace Law School in White Plains, N.Y., and an expert on the entrapment defense.
Guilty verdicts were set aside on those grounds for just three of 26 Abscam defendants.
"Stings work, and they get convictions," said Bruce Ledewitz, a professor at Duquesne University Law School, discussing the general tactic. "It's how public-corruption cases go forward."
The hard part for prosecutors is proving that gifts or money were bribes, that there was a trade-off, such as a lawmaker agreeing to change a vote or introduce a bill.
In Abscam and other cases, he noted, lawmakers were convicted when prosecutors could show they took an action in response to a bribe.
If evidence is tainted at the start by improper investigative tactics - in this case Kane said it was tainted by racism - it can destroy any possibility of winning in court, said Michael A. Schwartz, who until 2008 led the U.S. Attorney's corruption unit and oversaw the successful prosecution of former city treasurer Corey Kemp and former Councilman Rick Mariano.
He recalled that in one case, after winning in court, he later asked a judge to reverse the conviction because he found flaws in the investigation.
"It's not the slam dunk that one would assume just from the assertion 'We have people taking money on tape,' " said Robert Power, a Widener University law professor and former trial lawyer in the Justice Department's Organized Crime and Racketeering Section.
"Juries are reluctant to convict on just gifts," he said. "They sort of hold their nose, 'Politicians take gifts all the time.' Without an actual bribe, it's tough to make those cases with a questionable key witness."
Power said he wants to know exactly why the case went moribund, why it could not have been continued by introducing a clean undercover agent.
McElhatton said that if the case was truly so compromised that it could not go forward, then the attorney general should present the public with those facts.
"Lay it out there for us," he said. "When elected officials take money, they taint the entire process. Now it appears these folks that have taken money are going to get a pass. That doesn't sit right with me."
Inquirer staff writer Craig R. McCoy contributed to this article.