WASHINGTON (AP) — Investigators believe a shooting that damaged power substations in North Carolina was a crime. What they haven't named yet is a suspect or a motive.

Whatever the reason, the shooting serves as a reminder of why experts have stressed the need to secure the U.S. power grid. Authorities have warned that the nation's electricity infrastructure could be vulnerable targets for domestic terrorists.

Tens of thousands of people lost their electricity over the weekend after one or more people opened fire on two Duke Energy substations in Moore County, which is roughly 60 miles southwes...