Former Philadelphia narcotics squad officer Jeffrey Walker made a bet that helping the government out was the right thing to do. But, in his case, it means he'll spend another 15 months in prison.

U.S. District Court Judge Eduardo Robreno sentenced Walker to 42 months behind bars for pleading guilty to corruption, but Walker has already served more than two years in prison since his arrest in 2013. That time will be applied to his sentence. 

The FBI interviewed Walker more than 30 times in the lead-up to the indictment of six of his fellow officers, and he "provided an insider's view" of the alleged corruption prosecutors were attempting to ferret out, Assistant U.S. Attorney Anthony Wzorek said at Wednesday's sentencing hearing.

Helping out the prosecutors, Wzorek said, "broke the institutional code of silence" within the police force. Without Walker, prosecutors said, the indictment against the six would not have been possible.

That cooperation was considered in calculating an appropriate punishment for Walker, Judge Robreno said. After leaving prison, Walker will be on probation for three years. The judge also imposed a $5,000 fine.

"I have no excuses," said Walker, taking long pauses and choking back tears. "I want to apologize to the police commissioner for my behavior."

He also apologized to the police force and the communities his work impacted.

"I'm deeply sorry for my actions. I can't take it back," Walker said.

Federal authorities arrested him in 2013 following a sting that found him planting drugs in a car to build a bogus case. Authorities say he stole house keys from the suspect, then pilfered $15,000 from the suspect's house. When Walker exited the house with the money, federal authorities arrest him.

It's the kind of thuglike activity, he later testified during the trial, that his six former colleagues took part in regularly.

Federal prosecutors positioned Walker as their star witness in establishing a case.

But defense attorneys portrayed Walker as an unreliable source who stole and lied on his own without involving his six former colleagues, calling Walker's credibility and motives into question.

Walker, who spent more than two decades on the city's narcotics force, admitted in April to reckless activity that made him richer and locked up suspects on fake pretenses.

The lone-actor argument seemed to have helped sway the federal jury.

Earlier this month, the six officers were found not guilty on all charges. Meanwhile, Walker's corruption case has been moving along on a separate track.

Since a federal jury found the six officers in the case not guilty, should Walker's testimony be discounted? At Wednesday's hearing, Judge Robreno said not necessarily so.

He said Walker's testimony was "truthful and reliable," and that other witnesses, some of them drug dealers, backed it up.

Robreno then cited statements made by defense attorney Jack McMahon, who fought the government in this case, to the effect that finding a defendant not guilty is not the same as finding him innocent, and that if guilt isn't proved beyond a reasonable doubt, a not guilty verdict is justified.

In other words, Robreno said it's possible that Walker was telling the whole truth, but that doesn't undermine or change the jury's acquittal of the six.

The former narcotics squad officers have triggered some 150 civil lawsuits claiming they ran wild across the city abusing drug dealers, planting evidence and falsifying official police records to cover  their tracks.

A state judge has thrown out 400 convictions linked to the work of the six officers, a process being spearheaded by Philadelphia's public defender's office, which maintains that hundreds of others cases need to be re-examined in light of the six weeks of testimony that was revealed during the trial.

And this week, five of the six officers filed a defamation suit against the city's top officials for making statements they claim have tarnished their records and lives. The six are back on the police force but have been reassigned to district positions, rather than rejoining the narcotics squad.

Walker's attorney, Thomas Fitzpatrick, said that once his client is, "it goes without saying" he will not try to return to Philadelphia's police force.

"Jeffrey Walker did the best that he could do to redeem himself," Fitzpatrick said after the hearing. "Which is to do an about-face and tell the truth about the things that had occurred."