Police officers in the US have in 2015 killed at least 28 people holding BB or pellet guns comparable to the one Tamir Rice was carrying when he was shot dead in Cleveland, Ohio.

The steady stream of fatalities, recorded by a Guardian investigation into all deaths caused by law enforcement, has prompted some lawmakers and campaigners to push for tighter regulations on the design of non-lethal guns that often closely resemble real firearms.

Announcing on Monday that the officers involved in Rice’s November 2014 death would not face criminal charges, the Cuyahoga County prosecutor, Timothy McGinty, said: “I want to call on the legislature and the manufacturers of toy guns not to make guns that look so much like the real thing.”

On Friday, a new law aiming to ensure this will go into effect in California. It bars the sale of BB guns unless the “entire exterior surface of the device is white, bright red, bright orange, bright yellow, bright green, bright blue, bright pink, or bright purple, either singly or as the predominant color in combination with other colors in any pattern”, or it is transparent.

Support for the measure, which was signed in September last year by Governor Jerry Brown, increased after the fatal shooting by police in Sonoma County of Andy Lopez, a 13-year-old boy who was carrying a plastic toy gun that resembled an AK-47 rifle.

Local activist Marni Wroth said in the wake of Andy’s death regulating toy guns has never been a priority for activists, who have instead prioritized advocating for greater oversight of police use of force. Wroth said McGinty was “deflecting” by calling on toy gun manufacturers to change, and that the primary issue remained with police policy.

“That, to me, is just a smoke and mirrors thing,” she said.

The sheriff’s deputy who killed Lopez in October 2013 said that the barrel of Lopez’s toy gun moved towards him and another officer when Lopez turned around, after the deputy shouted at him to drop the weapon. That officer, Erick Gelhaus, didn’t face any criminal charges.

About nine months later, 22-year-old John Crawford was shot dead in a Walmart superstore near Dayton, Ohio, while speaking on his cellphone and holding a pellet rifle he had picked up from a shelf. Surveillance footage showed Crawford was shot almost instantly as he tried to run away when an armed officer advancing down an aisle towards him shouted an order. A grand jury decided not to indict the officers in that case.

Several deaths this year involved people who placed officers in difficult situations by wielding pellet guns while allegedly pretending to be armed with a genuine firearm. But other cases have raised more questions about the actions of responding officers.

Tiano Meton was killed by Border Patrol agents in January after refusing to stop at a checkpoint in Texas, authorities said. Officers pursued Meton for about 30 miles before Meton drove off the road. When agents approached Meton’s stopped car, one yelled “gun!” prompting two agents to open fire, according to the Hudspeth County Herald. Investigators later said that a “pistol-shaped pellet gun” was found in Meton’s car.

Deputies in San Bernardino county killed Ernesto Flores in April after family members called police when Flores set his sofa on fire, according to officials. Flores’ daughter said she told the emergency dispatcher that her father was armed with a pellet gun. Flores allegedly pointed the pellet rifle at responding deputies, who fired beanbag rounds before fatally shooting Flores.