A 17-year-old Lynnwood boy accused of accompanying two adults in the setting of a $4.5 million Edmonds fire was charged Monday with first-degree arson in Snohomish County Juvenile Court.

The boy, who has not been arrested, is scheduled to appear in court in about 10 days, deputy prosecutor John Stansell said.

Stansell said the boy has been cooperating with authorities. Two adults who allegedly accompanied him have been charged with arson in U.S. District Court. A 16-year-old girl who also may have been with the others has not been charged, Stansell added.

The Dec. 17 fire destroyed a building that would have had 28 condominium units and retail space on Fifth Avenue S. in Edmonds. The 90,000-square-foot building was about 70 percent complete.

Owner Bob Gregg said he’s put in a $4.5 million insurance claim, and he probably will suffer out-of-pocket expenses of another $500,000.

Edmonds police got a break in the case when one of the defendants bragged about setting the fire to a friend, Stansell alleged. The friend called police.

The Lynnwood boy told investigators that he and the adult defendants made plans to make and set off Molotov cocktails while attending a party in the hours before the fire. They gathered gasoline, orange juice and other materials in an attempt to make three homemade napalm devices.

One was thrown at a billboard on Highway 99 and the second on an Edmonds street. Neither ignited, Stansell said. The third was thrown at Gregg’s building, known as The Gregory.

It didn’t ignite either, so the Lynnwood youth announced that they should burn down the complex, Stansell said. They filled a 64-ounce juice container with gasoline, poured it on an interior stairwell and lit it, Stansell alleged.

The group left, but returned to find the fire still not burning much. Then, more combustible materials were added to fuel the fire, Stansell alleged.

“They then left again to get food at a fast-food restaurant,” Stansell said.

After eating they came back to find the complex ablaze.

“The group then went to a place with a suitable view of the fire,” Stansell said. “The group admired their handiwork from their vantage point.”

Reporter Jim Haley: 425-339-3447 or haley@heraldnet.com.