U.S. Attorney Richard Callahan said today that the federal investigation of the St. Louis towing scandal is ending with this morning's sentencing of its fourth and final figure to go to prison.

"All investigative leads have been fully explored and followed," he said in a prepared statement. "What is provable has been charged and what is not provable has not. No additional criminal charges are anticipated."

It is apparently a frustrating end for his office, given heated accusations in court today by Callahan's assistant on the case, Hal Goldsmith. He claimed that Kevin Shade, a city police officer snared in the probe and up for sentencing, had withdrawn cooperation that might have led further.

Shade was sentenced to 27 months in prison after U.S. District Judge Rodney Sippel said there were grounds to increase the penalty beyond the 21-month maximum that ordinarily would apply to someone with Shade's background.

Police Chief Dan Isom initially indicated today that he was hoping for "closure" but later issued a statement saying the department would look at the evidence to see if any internal action is indicated.

Court documents filed by the FBI indicated suspicions that some officers had accepted bribes or improper favors from the department's towing contractor.

The sentencing hearing turned hot over whether Shade, who has since left the police force, was trying to minimize his involvement in the crime.

A clearly frustrated judge complained at one point that defense lawyer Adam Fein's parsing of words about what his client did "defies common sense."

"Everything you've done today is trying to minimize his involvement -- he took money, but it was 'gratuities,'" Sippel said. "Come on!"

He added: "Either Mr. Shade lied to me when he pleaded guilty ... or you are lying to me now."

The former detective is the only proven link between the St. Louis police and a fraud scheme by St. Louis Metropolitan Towing, which held a contract to tow and impound cars for the department.

Shade, 36, pleaded guilty in August 2009 to a single felony charge of mail fraud, admitting that he accepted bribes as a police officer to falsify inspection records for impounded vehicles so they could fetch a higher price when resold through the company's affiliated businesses.

Goldsmith said Shade had been "key" to the federal investigation into the towing business, and blamed Shade's "flip flop ... for really throwing the government's prosecution of a related case and its investigation into a tizzy."

Goldsmith told the court "...it has had an extremely adverse impact on the government's investigation, an extremely adverse impact on the government's prosecution of related cases."

Former city police officer and Metropolitan Towing manager Gregory P. Shepard, identified by prosecutors as the mastermind of the fraud scheme, was sentenced last week to 10 months in prison on mail fraud and bribery charges.

Officials said the company had illicitly blocked owners of impounded cars from reclaiming them, and then resold the cars with falsified titles. It was Shepard who paid Shade for his help, according to the charges.

Kenneth and William Bialczak who own the parent company, S&H Parking Systems, were not accused in the fraud case but each received sentences of one year and one day in federal prison for failing to pay taxes on almost $1 million of income between them.

Reflecting on the case, Callahan, the U.S. attorney, noted that "not all allegations are true and not all true allegations are provable."

He continued, "I also want to remind the public that the vast majority of the men and women who work in the St. Louis police department are honorable human beings who deserve our respect and gratitude for the job they do. The acts of a few bad officers should not tarnish an entire department."