John Breen was the son of Lawrence's first Irish-American mayor. An undertaker by trade and an ex-alderman, Breen also served on the Lawrence School Committee at the time of the strike. He was arrested on Monday morning January 29, 1912, and accused of planting dynamite in three locations that were popular strikers' meeting places, one of which was the Urbano Di Prato First Class Shoe Repair shop. Upon discovery of the dynamite, strikers were arrested but quickly exonerated when police examined the newspaper used to wrap the dynamite. It was the popular undertakers' trade journal titled "Shadyside" with John Breen's name adorning the subscription label. Breen had been the one to tip off the police to the location of the dynamite.
Breen was arrested and later released on bail. His trial in May saw him convicted of planting dynamite to discredit the strikers but was fined only $500. Strikers were outraged and later found that Breen had been the pawn in an intricate conspiracy with ties to William Wood, president of the American Woolen Company.