One of the last three suspects in the $50,000 Coop stickup eluded a carefully set police trap yesterday morning, speeding away from his North Cambridge home and outdistancing squad cars despite road blocks in a dozen nearby communities.

The man, identified as a 37-year-old ex-convict, is one of three missing gunmen, the only participants in the January 9 robbery not yet rounded up, police disclosed. Apparently suspicious at the sight of patrol cars cruising in his area, the suspect dashed to his garage and escaped the police net in a tan automobile bearing Florida plates.

Blocked Roads Futile

As the car roared down Huron Avenue, hasty radio calls to Boston, Belmont, Somerville, Watertown, and other local communities set up road blocks along possible escape routes, but without success.

Police believe that the ex-convict had recently returned from Florida after seeing Anthony Novicki, the Dedham trigger-man in the holdup, who was arrested in Miami Tuesday. Miami authorities alleged that the Tilley couple of Boston, also arraigned Tuesday, had flown to Florida bearing funds to bolster Novicki's spotty finances.