The revelation that the man accused of detonating a homemade pipe bomb in New York City downloaded information from the internet on how to build such a device prompted New York Gov. Andrew Cuomo to urge Internet companies to reassess their approach to extremist content.

Akayed Ullah, a 27-year-old electrical worker from Bangladesh, detonated a homemade pipe bomb in an underground tunnel that connects to the crowded Times Square subway hub, police said. The explosive fizzled and injured three people in addition to burning Mr....