Myron Matthews was 18 at the time of his first conviction for illegal gun possession in 1997. A judge sentenced the Baltimore man to three years in prison but suspended all but three months. As a result, Mr. Matthews was back on the street within weeks.

A year later he was re-arrested on gun charges and again sentenced to three years. But this time he served only nine months, with the rest suspended. And over the next decade Mr. Matthews would be in and out of jail for a half dozen more robbery and gun crimes, each time serving only a fraction of his sentence.

His story is typical of what Baltimore Mayor Stephanie Rawlings-Blake has called a revolving door for gun offenders, a criminal justice system that allows a relatively small but hardened core of career criminals to terrorize their fellow citizens with impunity. Even when the state's gun laws are enforced, these offenders are able to bargain with judges and prosecutors to obtain sentences so watered down as to no longer be meaningful as deterrents. Their time in prison or jail is mere prelude to their next crime spree.

A year after Mr. Matthews' second arrest, for example, he was re-arrested for gun possession in 1999, and the following year he was also convicted of armed robbery. The cases were combined, and he received a total of 11 years for the two crimes. But he served only a fraction of that time before being released.

Police and prosecutors know that defendants like Mr. Matthews are responsible for most of the city's violent crimes, but they feel powerless to keep them behind bars. Forty-four percent of Baltimore homicides are committed by people with previous convictions for gun possession. As Baltimore Police Commissioner Frederick H. Bealefeld III pointed out at a news conference this week, if those offenders had been kept behind bars the city would have had 80 fewer homicides in 2010. Getting illegal guns and the people who use them off the streets is the key to reducing the number of murders, non-fatal shootings and juvenile homicides in Baltimore.

But for that to happen, police and prosecutors need the tools to keep bad guys with guns locked up for more than just a few weeks or months. At the same press conference where Commissioner Bealefeld spoke, Ms. Rawlings-Blake renewed her call to lawmakers in Annapolis to raise the minimum sentence for felons who carry guns to five years and to make first-time possession of an illegal gun a felony rather than a misdemeanor, with a mandatory minimum sentence of 18 months.

Lawmakers have often been reluctant to enact minimum sentencing laws, fearing they would deprive judges of the discretion to impose appropriate penalties. That makes sense when the offense involves low-level drug offenses or nonviolent property crimes. But gun offenders are different, not only because they are more likely to use a gun in a crime of violence but because they are more likely to continue committing such crimes. Penalties that amount to little more than a slap on the wrist put everyone in their communities at risk.

So it was with Mr. Matthews. After he got out of prison in 2004, he immediately went back to his old ways. Within a year he had racked up two more arrests and convictions on gun charges, and again the cases were combined. In 2005, he received a five-year sentence for both crimes. After serving his time he returned to Baltimore, and in August he was arrested there for handgun possession. His case is currently awaiting adjudication in Baltimore City Circuit Court.