A middle-aged man who works at the market complained that it made no sense to him why anyone would put a bomb in a crowded vegetable market: He said that all the traders and sellers were going about their business when the explosion took place.
VOA: standard.2009.06.01
Two sections of the Patriot Act the "lone wolf" provision and "roving wiretaps" (both requiring authorization by a special court) were created precisely to identify and monitor an individual like Tamerlan Tsarnaev before he detonates a bomb inacrowded public place.
That seems unlikely, given that one of the experiments with a positive result was conducted ina remote area of China while another that had a negative result took placein Belgium, one of the most crowded parts of the planet.