The Boston Marathon bombers had planned to detonate their remaining explosives in New York City's Times Square, law enforcement officials told US network NBC News.
Dzhokhar Tsarnaev had initially told questioners in hospital that he and his brother were planning to go to New York to "party", but later changed his story to say they wanted to explode more bombs.
One senior official told NBC News that the Tsarnaev brothers' plan was "undeveloped and aspirational at most."
More top news
Rescue workers are at the site Sunday morning trying to cut open mangled coaches.
Despite chilly temperatures it will be a mostly dry day, and milder than yesterday.
The Sunday Times alleges a missile malfunctioned after launch during a routine test of the UK's nuclear deterrent last year.