BREWSTER — They stared in disbelief at the charred remnants of the place where they had worshiped. They wept at the sight of blackened rubble strewn over lawns up to 100 yards away. The parishioners of the Cape Cod Bible Alliance Church in Brewster struggled to understand why someone set the blaze early Friday that destroyed the 25-year-old building on Main Street.

Authorities believe they know how it happened. They arrested Adam Finnegan, 29, of Brewster, on a charge of setting the fast-spreading three-alarm blaze that broke out around 3 a.m. Friday, according to State Fire Marshal Stephen D. Coan.