The Tracy Police Department urges residents to have patience as it works through a dreadful December following the arrest of three men after a gang-related shooting Friday night that left a 21-year-old Tracy man dead.

Tracy police spokesman Sgt. Tony Sheneman said five homicides in 2009 have given Tracy a little more attention as a dangerous place. That’s the highest number in memory, and the most since there were three killings in 1997. No one was slain last year.

He said that even though gang prevention officers are working tirelessly, not everything can be prevented. Sheneman said officers can’t just toss someone in jail because they look the part.

“Our concentration on gang enforcement is just as strong as it was before,” Sheneman said. “We can’t stop someone on the street, put them against the wall and search them without reasonable suspicion that a crime has been committed. We can’t arrest them without probable cause.”

The latest gang-related violence was Friday night, when a 16-year-old boy was shot and a 21-year-old man, Spencer Sampson, was killed in eastern Tracy.

Over the weekend, Roberto Arias Jr., 19, Martin Flores, 21, and Armando Hernandez-Valencia, 20, were arrested on suspicion of homicide in connection with the shooting.

While Sheneman said the men who were taken into custody were members of the Sureño gang, Sampson’s wife said he was uninvolved in gang life. Sheneman also confirmed that Sampson is not in the police database of known gang members.

Many Tracy residents have been worried about the direction the city is headed in after four drive-by shootings in two days this month and a string of armed robberies of markets and banks.

On Dec. 16, a group of men with black bandanas over their faces was responsible for three shootings, including one at Tracy Garden Apartments that put a man in the hospital with bullet wounds to his upper torso.

Police said the men drove away in a dark SUV, but Sheneman didn’t have a better description of the vehicle beyond that.

He also said he was unsure whether that was in retaliation for another gang-related drive-by on Dec. 4, when a man in a gold GMC Yukon shot a man twice in the leg on Holly Drive, near Grant Line Road.

In October, a man died from a gunshot to the head after a known gang member opened fire through the door of Amore’s Italian Restaurant, but Sheneman said that was not a gang-on-gang crime.

“Have we seen an increase in what we believe is gang-related violence? Yes, we have,” he said.

In November, Sgt. Terry Miller, who leads the city’s anti-gang enforcement, said there are more than 600 documented gang members in the department’s database, most of whom live in Tracy. Miller said then that 160 were in custody.

His gang unit goes to schools and sometimes to homes to head off signs of gang activity while kids are young and susceptible to recruitment. Miller said the unit also works closely with patrol officers to watch for suspicious activity and track down known gang members.

Though there has been a spat of violence recently, Sheneman said that, aside from homicides, there has been no major uptick in crime. Last year, Tracy had 66 robberies. So far this year, there have been 66, he said, although 11 came this December compared with five robberies in December of 2008.

Sheneman said that between five and seven people wearing masks have been responsible for a string of armed robberies this month of Taco Bell, Pizza Hut, Quik Stop and three banks.

Ripon police arrested two people Wednesday who Sheneman said robbed banks in Tracy’s Save Mart and Safeway supermarkets, though he noted that those suspects are not connected to the masked bandits.

Sheneman added that police have identified many of the people involved, and some of them are underage.

“This is something that we take very seriously,” he said. “It’s difficult to stop — in fact, it’s darn near impossible to stop — random acts of violence.”