These are items the Santa Clara County District Attorney's Office said are being fired at buildings, homes and cars at potentially lethal speeds.
"These aren't ball bearings that are small, these are the size of a quarter that are going over 100 miles per hour," Captain Michael Whittington with the Bureau of Investigation for the Santa Clara County DA's Office told ABC7 News.
Capt. Whittington said behavior by the person or people responsible is only getting worse. He said the crime is now coming off the freeway.
Whittington explained that just two weeks ago, a woman in her car was targeted and had her windows blown out.
"Unacceptable, definitely unacceptable," San Jose resident Tong Tran said, reacting to the crime.
Resident Mario Hernandez called the actions reckless.
"Definitely reckless behavior," he said. "And if they're doing it just for fun, they have to think about the fact that somebody can get hurt. And not just minor, but severe injuries. If it's a ball bearing, it could be deadly."
Some residents living along the Hwy 87 corridor said the potential danger is enough to make them consider a detour.
"That makes me not really want to take the 87 anymore, hearing about the ball bearings," Tran told ABC7 News. "I might have to take like the 101 just to go back home, and take the inside roads after that."
The DA's Office said there has been nearly 30 incidents since March. The office's Crime Lab was reportedly struck eight times.
Farther from Highway 87, the SAP Center and the San Jose Museum of Art also saw damage.
Investigators explained the person is using a slingshot to launch metal ball bearings, mainly between the hours of 9 p.m. and 6 a.m. Capt. Whittington said the suspect has already caused more than half a million dollars in damage.
DA Jeff Rosen said this is not just property damage. Adding, "People live and work behind those windows."
"Imagine, for our people in the community," Capt. Whittington spelled out. "You're driving your car and this silent ball bearing comes in your window and hits you. It will kill you."
With safety in mind, the DA's Office announced it has joined with other victims to offer a $20,000 reward in the search for the "Highway Slingshot Shooter."
The reward money is funded by a community driven partnership with the Silicon Valley Crime Stoppers.
As stated in the DA's Office release: If you have information about this crime you can submit anonymous crime tip information using Silicon Valley Crime Stoppers P3TIPS mobile app, by calling the tip line at (408) 947-STOP, or online at www.svcrimestoppers.org. If the information you submit leads to an arrest you are eligible for the reward.