TACOMA, Wash. (NewsNation) — Power is back on for thousands of people in the Tacoma, Washington, area after a series of attacks left families in the dark on Christmas Day.

Officials warn, however, a threat to the power grid remains.

Four substations were broken into and vandalized, which knocked out power for nearly 14,000 customers, according to deputies.

Officials in Pierce County on Tuesday said they are using evidence collected from some of the scenes, including surveillance video, to try and identify a suspect.

“Looking at it from an outside perspective, these all seem related because of the area that they’re in. They’re all pretty close,” said Sgt. Darren Moss Jr. of the Pierce County Sheriff’s Office.

The reported attacks have added to the substations targeted across the country.

In the last few months, power companies reported confirmed attacks or intrusions in Washington, Oregon, North Carolina and Florida. No one has claimed responsibility and law enforcement has not named any suspects.

Tacoma Power, which operates two of the targeted stations said in part: “Tacoma Power follows federal reliability standards, including assessing physical risks to our critical energy infrastructure and applying recommended mitigation measures.”

In April 2013, gunmen in Coyote, California, shot at 17 electrical transformers causing $15 million worth of damage. The attackers were never found, but the incident exposed a significant vulnerability in the nation’s power infrastructure. In response, federal regulators established mandatory physical security standards in 2015.

But those federal standards haven’t been significantly updated since then, although now they are under review.

Detailed location information on substations can be easily found on the internet.

According to some researchers on domestic extremism, that information has circulated chat rooms involving suspected white supremacists who celebrate and encourage more attacks.

Experts say these physical security threats are not something most utility companies are used to preparing for.

“The power company is focused on safety, not necessarily security, not necessarily protecting against someone with the intent to go into a substation to disable that substation,” said Todd Keil, an associate managing director for security risk management at Kroll, who previously worked with the U.S. Department of Homeland Security (DHS).

NewsNation reporter Andrew Dorn contributed to this report.