TAMPA — Twice as many people have been shot to death in Tampa in 2015 than in the first three months of last year. Some of the victims have been students in local schools. In a number of cases, witnesses have refused to cooperate with police.

Chief Jane Castor highlighted the alarming surge in gun violence at a Monday news conference, calling particular attention to the youth of some of the victims, and pleading for the public's help.

"What we need is for the community to get angry about what is happening in our back yard," Castor said. "Our kids are being killed, and we've got to stop this."

Castor gave a series of statistics to illustrate the extent of the problem.

• In the first three months of 2014, police classified 22 incidents as "aggravated batteries with a gun." This year, the number has grown to 48.

• Police documented a total of 164 gun crimes at this time last year compared to 235 this year.

• Homicides more than doubled from seven to 15 over the same time period.

In addition to shootings, police have also documented more than double the number of guns reported stolen along with a significant increase in the number of guns recovered.

Of particular concern, Castor said, is the number of crimes that have involved school-aged kids. The chief spoke specifically about three teenage boys who died in separate shootings in the last two weeks.

Richard Newton, 14, was killed Saturday night when someone fired a gun after a fight broke out at a north Tampa birthday party. No arrest has been made.

Likewise, detectives have yet to make an arrest in the death of 16-year-old Jamylin Turner, who was killed a week earlier in a drive-by shooting as he was playing basketball with friends near Robles Park. The same day, Ikeim Boswell, also 16, died after one of his friends accidentally shot him in the neck while showing off a gun behind a Sulphur Springs house.

Newton, Turner, and Boswell all attended local schools.

Hillsborough School Board member Doretha Edgecomb and acting superintendent Jeff Eakins appeared with Castor to call attention to the shootings.

"It is important for us to understand and to tell the story that our students really matter and that they aren't just numbers. They have names. They belong to families," Edgecomb said. "Please, please, if you know anything about this, please come forward. Because if you don't, this is going to continue."

While some of the shootings occurred in the same areas of town, Castor could not say whether any of them were related.

She noted at least four of this year's shootings have been deemed accidental. At least one other was seen as a possible case of self-defense.

As for why the city is seeing such a sharp increase in gun violence, Castor couldn't explain. In some cases, drugs are involved. Others were sparked by "territorial disputes," the chief said, though she stopped short of calling them gang-related.

"There's never any rhyme or reason," she said. "It's one of those things that keeps us on our toes in law enforcement. There's very little predictability to it."

But one commonality is clear: a reluctance to help police.

"What has not changed, unfortunately, is that we get very little cooperation from the witnesses and, in most cases, the victims," Castor said. "The citizens have got to work with the Police Department in order to stop this violence."

Contact Dan Sullivan at dsullivan@tampabay.com or (813) 226-3386. Follow @TimesDan.