A fire on Monday caused $100,000 in damage to a home being built on East Laurel Road. Fire Inspector Bill Hewett called the fire "suspicious."

Video: Investigators Explore Link Between Fires

A fire on July 20 destroyed a home under construction on Chuckanut Drive, and accidental causes were ruled out.

Investigators are trying to find evidence to see if have a serial arsonist on their hands, KIRO 7 Eyewitness News North Sound Bureau Chief Anna Velasquez reported.

Investigators are also looking into whether eco-terrorists are trying to send a message.

In April, a new home in Sammamish burned. A sign nearby that read "where are all the trees, burn rapist burn, ELF" suggested a link to the Earth Liberation Front, a group that has used fires in the past to protest development.

A $10,000 reward is being offered for information leading to an arrest.