Sonoma County sheriff's detectives are boosting their presence in the Sonoma Valley after an alarming string of gang-related burglaries, robberies, assaults, a shooting and a stabbing.

Detectives have seized more than 15 guns and arrested at least 13 individuals in April for crimes ranging from assault and indecent exposure to robbery and possessing stolen firearms, Sgt. Dave Pedersen said.

Investigators suspect many of the crimes have been committed by members of the same norte? gang, long active in the Sonoma Valley.

"It's been heating up," said Pedersen, who runs Sonoma County's Multi-Agency Gang Enforcement Team.

The incidents include the March 29 beating and robbery of a gay Sonoma teen at El Verano School, shots fired April 5 at a nearby Taco Bell and several neighborhood burglaries.

But the violence is not all recent.

An 18-year-old member of the same group was repeatedly stabbed Oct. 22 during a fight with rival gang members during an annual memorial held for teen slain in 2007, Pedersen said.

Pedersen said there is no clear reason for what appears to be a crime spree.

The gang unit is stepping up its efforts to arrest gang members committing crimes and to get guns off the street, Pedersen said. They are researching each of the weapons seized and have so far determined several were stolen.

"Gang members and gangs in general deal with fear and intimidation. Guns are a hot commodity," Pedersen said.

On Friday, detectives arrested a 51-year-old man suspected of selling a 9 mm pistol to a man he knew belonged to this gang, Pedersen said.

They suspect Dilip Kumar Sinha sold the weapon for $200 to a bakery coworker, Daniel Chavarria, 26, of Sonoma, an alleged gang member, Pedersen said.

Chavarria came under investigation after he was seen with a group of males near the Nissan Frontier pickup used as a getaway car during the April 5 shooting, sheriff's officials said.

During that incident, a group of males taunted and exposed their genitals to a security guard who confronted them at Maxwell Farms Regional Park. Startled bystanders moments later heard several shots and saw "muzzle flash" at the Taco Bell. The Nissan pickup truck was seen speeding away. Detectives found 9 mm shell casings in the gutter.

After Chavarria was seen near the Nissan the next week and arrested, detectives searched his bedroom, where they found Sinha's 9 mm pistol attached with Velcro under a chair, Pedersen said.

Sinha originally told deputies that he lost the gun while he was duck hunting near Millerick Road, Pedersen said.

A loaded Colt .380 semi-automatic pistol stolen Thursday during a residential burglary on Jami Lee Lane in El Verano turned up the next day when a deputy on patrol searched a backpack next to four teenagers found drinking beer in Maxwell Park, Pedersen said.

The Colt was just one of three semi-automatic weapons stolen during the residential burglary, Pedersen said. Jewelry, a laptop computer, a video game console, a rare-coin collection as well as valuable baseball and basketball card collections were also taken.

Witnesses "saw two teenagers pulling the neighbor's garbage can down the street" from the burglarized house, according to Pedersen.

Five guns deputies seized April 13 had been stolen the day before during another residential burglary in El Verano: two rifles, a shotgun, a handgun and a .357 handgun, according to the Sheriff's Office.

You can reach Staff Writer Julie Johnson at 521-5220 or julie.johnson@pressdemocrat.com. On Twitter @jjpressdem.