LYNNWOOD — It’s not only a whodunit, it’s a whydunit.

Vandals with chainsaws attacked five Snohomish County PUD power poles in two separate incidents over the past week. They were about a mile apart, both near the Interurban Trail in Lynnwood.

“They actually cut a pole down with a chainsaw,” said Aaron Swaney, a PUD spokesman. “Then we found four more poles with cuts in them.”

The utility is working with law enforcement — including the Seattle office of the FBI— and is seeking help from the public.

“We don’t know the motives for this vandalism,” Swaney said. “Whether someone is doing it just to damage our infrastructure or if they have more sinister motives — all we know is that this is potentially very dangerous.”

The incidents were also reported to the Lynnwood Police Department, Snohomish County Sheriff’s Office, federal Department of Energy and state power companies.

“It’s something we’ve never really seen before,” Swaney said. “We haven’t heard of any other utilities this is happening to.”

These are unlike theft cases in which the motive is to profit by stealing scrap metal, such as copper wire, to sell.

“Nothing was stolen off the pole, nothing taken, so it’s really just vandalism, which is concerning and strange,” Swaney said. “It’s hard to tell from the cuts whether they are proficient with a chainsaw or just out there hacking away at something.”

The downed power pole was cut early Friday near Butternut Road and Maple Road. It caused an outage affecting 4,000 customers.

A Facebook post from a nearby resident said: “It is 1:00 a.m. and my household … is woken up by a massive crash noise. Then all power goes out for our neighborhood. The pole is surrounded by saw dust. I don’t understand what would motivate someone to go around cutting down power poles?”

Photos on the post show the severed pole on the ground.

On Saturday, PUD security guards discovered four power poles with chainsaw slashes near an I-5 on-ramp not far from the North Alderwood substation. It caused limited power outages. The poles did not fall.

“The guy wires were able to hold up the pole,” Swaney said. “What’s worrisome for us is that it is so close to I-5. That enters another category of danger. If things were to go wrong you could have wires down on a major highway.”

Swaney said it isn’t possible for the utility to monitor all sites.

“We have 112,000 poles in our service area in Snohomish County and Camano Island,” he said.

Patrols have been ramped up, with around-the-clock security on poles within a two-mile radius of the Lynnwood incidents.

“We take this type of vandalism extremely seriously,” Rob Beidler, PUD security manager, said in a news release. “Attempting to damage energized infrastructure is very dangerous and can result in severe injury or even death. We’re very fortunate no one was hurt in these incidents.”

The PUD is asking the public to be aware of suspicious activity near all substations or power poles. Anyone who sees or hears anything or with information on either of these incidents should call 9-1-1.

Herald reporter Ian Davis-Leonard contributed to this story.

Andrea Brown: abrown@heraldnet.com; 425-339-3443. Twitter @reporterbrown.