Seattle City Light says the 26 poles that fell along East Marginal Way South on April 5 "range significantly" in age. 

The oldest two were installed in 1954. The five newest were installed in 2011. They were all inspected in 2016. 

Additionally, eight of the poles were flagged for replacement, though they were not identified as needing to be replaced immediately at the time. They were included in the utility's improvement plan. 

City Light still doesn't know what caused the power poles to suddenly fall. One pole fell directly on Linda and Tom Cook's vehicle as they drove. 

RELATED: Traffic cameras capture moment power pole collapsed on car near Tukwila

The city is hiring a third-party investigator. However, it has been a "slower process than we'd hoped." 

"As we developed the scope of work and level of public scrutiny that this engagement would require, we realized that it was important to find a firm with the specific skills, capacity and interest to conduct a robust investigation in a timely manner," the city wrote. "We’ve had conversations with several firms and we’re now in discussion with a national engineering firm and plan to engage an appropriate firm as soon as possible."

It's unclear how long the investigation will take. 

“We’re going to be as transparent as possible,” Seattle City Light CEO and General Manager Debra Smith said following the incident. “As much information as we can share we will.”

RELATED: Power poles that collapsed in south Seattle were inspected 3 years ago