A renewed enforcement of a 10-year-old law has reaped big new benefits in San Francisco, where police cite it as a primary factor in a recent drop in homicides.

"Triggerlock," (search) as the federal law is known, allows police to arrest suspected violent criminals on lesser charges. After an arrest is made, police search the suspect for guns. If they find even one, the suspect can be sentenced to 10 years in prison, effectively keeping him or her off the street.

The San Francisco Police Department (search ) turned to the law in the wake of a spike in homicides in early 2004, which they say may have been due to a rise in gang activity, as opposed to increased numbers of criminals in the city.

Lt. John Murphy, (search ) who works in the department’s gang unit, said, “there was a handful of thugs who were basically killing people left and right and they didn’t care.” Cops said nabbing the suspects was the key to reducing the violence.

Cops credit Triggerlock with the success. After its implementation, the second half of 2004 saw marked drop in homicides, down to 35 from 53. Murphy cited the removal of gang members and leaders as chief among the successes of Triggerlock.

“The leaders are now doing a significant period of time and that’s what we’re looking to do, get rid of the leaders and get rid of the very serious hardcore criminals that were doing the shootings,” he said.

Some people, however, criticize the law for unnecessarily bringing minor gun offenders in for federal gun crimes.

“The ultimate sentence that is imposed tends to be much higher and the question is, ‘is that appropriate?’” said Public Defender Ron Tyler.

Click in the video box above to see a full report by Fox News' Claudia Cowan.