Was the Boston marathon bombing a domestic terrorist act or international?

The Boston Marathon bombing is primarily classified as a domestic terrorist act. It was carried out by two brothers, Tamerlan and Dzhokhar Tsarnaev, who were U.S. residents with Chechen heritage. While the attack had international implications due to the perpetrators' background and motivations, it was executed within the United States and targeted civilians during a public event, fitting the definition of domestic terrorism.