CHICAGO (NewsNation) — The suspect in Tuesday’s massacre at a Uvalde, Texas, elementary school was a teenager, as most school shooters have been over the past decade.

Since 1999, seven in 10 school shootings have been carried out by people under the age of 18, when counting cases where the shooter’s age was recorded, The Washington Post reported. The median age of school shooters is 16.

The youngest of these was a 6-year-old male first-grader, who shot his classmate in 2000 with a .32-caliber handgun after saying he didn’t like her. 

So, how are minors coming into possession of these weapons?

The majority of them purchase them legally, or they’re given to them as gifts from parents. Most of these shootings occurred in cities and states where they are legally allowed to own these weapons.

After a gunman killed 20 children and six adults at Sandy Hook Elementary in Newtown, Connecticut, in December 2012, the state passed some of the most restrictive gun laws in the country.

Aside from Connecticut, you must be over 21 to possess a handgun in Washington, Iowa, Illinois, New York, New Jersey, Massachusetts, Maryland, and Washington, D.C.

In most school shootings, the gunman died at the scene, most often by suicide. However, most of the school shooters had either expressed suicidal thoughts or had explicitly talked about suicide before their attack.

Scientific American analyzed 14 different school shootings and found only two of the students involved in school shootings had no direct tie to the school that they targeted.