'Ghost guns' showing up in school shootings, experts fear trend will get worse

Four recent shootings involved a gun made from an online kit, police said.

Since November, at least four school shootings had an alarming connection to law enforcement and activists alike; the suspected shooters used a "ghost gun."

A "ghost gun" is a firearm that comes packaged in parts, can be bought online and assembled without much of a trace, which experts warn are becoming increasingly dangerous.

"When we first heard about these weapons, we thought anyone can get them, even a kid. It's not a hypothetical anymore," Alex McCourt, an assistant professor with the Johns Hopkins Center for Gun Violence Prevention and Policy, told ABC News.

McCourt, law enforcement offices and other experts who have been studying the proliferation of "ghost guns" told ABC News this trend is likely to continue beyond the school setting unless policymakers take action.