SOUTH PORTLAND – A 23-year-old Yarmouth resident was arrested Thursday for a sex crime allegedly committed against a child in South Portland.

Ronald Grant Thurston III, a former firefighter, was arrested on one count of gross sexual assault, a class A felony. The alleged victim was under the age of 14.

Thurston is being held at the Cumberland County Jail in Portland. Bail was set at $5,000 cash, and jail officials said he was expected in court as soon as Friday, Jan. 20.

Police Lt. Frank Clark of South Portland said Westbrook police received information Wednesday that linked Thurston to the crime allegedly committed in South Portland last summer.

He said the Westbrook, Yarmouth and South Portland police departments conducted a joint investigation that included several interviews and the execution of a search warrant at Thurston’s home.

Clark said the investigation is continuing, but would not say if there other incidents under investigation, or in how many communities. He also did not provide the sex of the alleged victim in the South Portland case.

According to Thurston’s Facebook page, he graduated from Yarmouth High School in 2007 and served as a Yarmouth firefighter.

Amy Anderson can be reached at 781-3661 ext. 110 or aanderson@theforecaster.net. Follow Amy on Twitter: @amy_k_anderson.