Experts have called ghost guns the country’s fastest-growing gun safety problem. They have been increasingly used in high-profile shootings.

According to figures from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), 20,000 suspected ghost guns were reported as being found by law enforcement in criminal investigations in 2022 – a tenfold increase from 2016.

Authorities say that without serial numbers on their frames, it is virtually impossible to track dealers who are selling these guns illegally to minors or to people without licenses.

A former government official doubted whether people’s minds would be changed by Mr Thompson’s killing. “Ghost guns are a new factor in a very complicated and violent country,” Juliette Kayyem told BBC Radio 4’s Today programme.

America was finding it “very hard” to restrict the firearm, said Ms Kayyem, former assistant secretary for policy at the Department of Homeland Security.

More than 48,000 people were killed by firearms generally in the US in 2022, according to the Centers for Disease Control and Prevention (CDC).