CNN  — 

Investigators – who have found nearly two dozen shell casings from a high-powered rifle – are zeroing in on two threads of possible motives centered around extremist behavior for the weekend assault on two North Carolina electric substations, according to law-enforcement sources briefed on the investigation.

The news comes as the primary utility company in Moore County restored electricity to the final customers of the 45,000 homes and businesses that initially lost power.

Officials on Wednesday also announced a total of $75,000 in reward money for information leading to the arrest and conviction of the person or people responsible for Saturday’s attacks.