It's the guns, many of us say, arguing for sensible restrictions.

It's not the guns, others argue, but the failure of the criminal-justice system to keep violent thugs behind bars.

In the week since Liczbinski's murder, the either/or argument has become as predictable and nonproductive as the abortion debate. Typical are the responses to my column last week in which I lamented the availability of the assault weapon used to kill Liczbinski.

"The gun used is only the tool," wrote Lynn Wyman. "The three felons that killed officer Liczbinski already had many convictions, but justice in Philadelphia believes in releasing these criminals back onto the street to prey upon society."

"Instead of getting angry about guns, why don't you get upset at [Pennsylvania's] inability to keep felons in prison," wrote Craig Norris Jr.

"Where is your outrage at the fact that this man, a convicted felon, was a violent criminal who shouldn't have been out of jail in the first place?" wrote Oliver Gruber.

I don't know why the men charged in the murder were on the street.

I don't know if they were adequately sentenced on previous crimes, or if they served an appropriate amount of time on the sentences they received.

I don't know if they were considered high risk for violence when they were released - and what, if anything, was done about it.

I don't know what can be done about it, beyond probationary supervision and the re-entry support Mayor Nutter has made a priority.

But, frankly, I'd like to know.

I'd like to know because I'm tired of the argument.

I'd like to know because it would be more productive to debate facts than philosophies.

I'd like to know because - perhaps it could even help.

Should the men have been on the street? If not, can we fix it so the next potential cop-killers aren't?

Clearly, the public deserves answers to these questions.

And I think City Council should convene public hearings to provide them.

It would be a tribute to Sgt. Liczbinski and all the police officers who risk their lives every day.

Everett Gillison, deputy mayor for public safety, agrees that there's a need for answers.

"The mayor has asked me to find out what happened here," he told me yesterday.

"Was there a failure? And if there was - and I'm not going to suggest there was or wasn't - then how do we as an administration respond to it?

"I think the public has a right to know and I think there's an opportunity here to educate the public."

The outcry over this crime, however, demands a public inquiry, not just a private investigation.

Councilwoman Donna Reed Miller, head of City Council's Public Safety Committee, told me yesterday that she'd consider holding hearings.

Miller said that she briefly discussed the idea of public hearings with a legislative aide in response to my phone call.

"It's a thought and we're going to think about it," she said.

The truth is, of course, that there's nothing mutually exclusive about the proposed solutions to gun violence.

The adoption of reasonable gun restrictions doesn't preclude closing whatever loopholes might exist in the administration of justice.

While proponents of gun limits would no doubt agree with this, the gun lobby won't hear of it.

The solution, as many of them see it, is to keep felons behind bars - presumably forever.

Some of the folks who think that the Second Amendment is sacrosanct have little regard for other provisions of the Bill of Rights.

But throwing away the key isn't an option - not in this country anyway.

Prisoners are entitled to freedom once they pay their debt to society, as loathsome as some of them may be.

But the outcry over the murder of Sgt. Liczbinski demands answers to the accusation that the criminal justice system is at fault.

Because only specific answers can end the predictably futile debate about where to place the blame. *

E-mail porterj@phillynews.com or call 215-854-5850. For recent columns:

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