(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.
One thread involves the writings by extremists on online forums encouraging attacks on critical infrastructure. The second thread looks at a series of recent disruptions of LGBTQ+ events across the nation by domestic extremists.
The FBI and the NC State Bureau are assisting in the investigation.
investigators have no evidence connecting the North Carolina attacks to a drag event at the theater in the same county, but the timing of two events are being considered in context with the growing tensions and armed confrontations around similar LBGTQ+ events across the country, the sources told CNN.
In the past two years, anti-government groups began using online forums to urge followers to attack critical infrastructure, including the power grid. They have posted documents and even instructions outlining vulnerabilities and suggesting the use of high-powered rifles.
One 14-page guide obtained by CNN cited as an example the 2013 sniper attack on a high voltage substation at the edge of Silicon Valley that destroyed 17 transformers and cost Pacific Gas and Electric $15 million in repairs.
In that case, the shooter fired more than 100 bullets in about 20 minutes, disappearing a minute before police arrived. The case remains unsolved.
While investigators haven't found a rifle in the North Carolina shootings, the casings still could offer critical evidence. A law enforcement source told CNN that the caliber of the bullets in the California incident is different from those used in North Carolina.
Investigators are taking into consideration that the timing of Moore County shootings -- 7 p.m. on a Saturday night -- coincided with the time a drag performance sponsored by the local LBGTQ+ community began, according to the sources. Audience members used their phone flashlights to light the stage for one last song, but after that the performance couldn't continue due to the power outage, according to Sandhills PRIDE.
Officials have said the gunfire, which left much of the county without electricity for days, were a "malicious" and "intentional" attack. The two substations are about 10 miles apart.
No suspects in the outages have been announced.
Sheriff Ronnie Fields has said whoever fired at the substations "knew exactly what they were doing." No group "has stepped up to acknowledge or accept they're the ones who (did) it," the sheriff said Sunday.
As of Wednesday morning there were 35,000 customers without power, but that number had decreased to 1,200 by the time a 4 p.m. news conference began, according to Duke Energy spokesperson Jeff Brooks. A few hours later the company's website showed zero outages in the area.
Given the information, county officials said a nightly curfew will end for good at 5 a.m. Thursday.
Bullets recovered from the sites, and the brass shell casings found a short distance away, are the few pieces of physical evidence that investigators have.
Because of the heat generated in a high-powered rifle's chamber during rapid fire, fingerprints are burned away -- and nearly impossible to recover from spent casings. Still, the brass may offer valuable clues.
Investigators can enter the casings into the National Integrated Ballistic Information Network, a database from the Bureau of Alcohol, Tobacco, Firearms and Explosives. The database records three-dimensional images of shell casings and can match them to any other shell casings that may have been fired by the same gun at another crime scene or to the gun if the weapon is recovered.
The spot where the casings were found can give investigators a way to pinpoint the firing positions. Knowing where the shooter fired from could lead to discoveries such as shoe prints and tire tracks.
For now, schools are closed through Thursday, many stores and restaurants are shut, homes are without heating or running refrigerators, drivers are traversing intersections with no traffic lights.
A Red Cross-run emergency shelter was set up at the Moore County Sports Complex to help provide shelter, food, showers and other services to people impacted. It will remain as a shelter through noon on Thursday, officials said.
Nakasha Jackson, who came to the shelter to pick up some hot food, said the outage has been difficult for her 1-year-old child.
"No lights, no power, can't really do nothing. The kid is scared of the dark," she told CNN.
Jackson said sometimes she has to travel up to an hour one way to buy food. "It's ridiculous. It should never have been done," Jackson said.
Residents who rely on electricity-powered medical equipment have also seen their lives upended. One woman told CNN she came to the shelter because she had no power for her CPAP machine at night.
After two days of sleeping without it, she said she began to feel ill and came into the shelter for help.
Others have sought shelter fearing for their safety as they struggled to keep their homes warm.
"It's different. It's kind of hard to sleep, you know. But at the end of the day, I'd rather be somewhere where it's warm, where we have food, where we're taken care of than to be somewhere it's freezing cold," said Amber Sampson.
On top of having to stay at the shelter, Sampson hasn't been able to work since Sunday after her employer also lost power -- an issue that could end up costing her hundreds of dollars.
Authorities have expressed anger over the attack, with Carol Haney, mayor of Southern Pines -- a town of about 15,900 residents that completely lost power -- calling it a cruel and selfish act.
North Carolina Gov. Roy Cooper voiced concern over businesses and residents in nursing homes.
"When we look at all the money that's being lost by businesses here at Christmastime, when we look at threats to people in nursing homes having lost power, hospitals having to run off generators and not being able to do certain kinds of operations at this point -- all of those are deep concerns here, and we can't let this happen," the Democrat told CNN on Tuesday.
"This was a malicious, criminal attack on the entire community."