Photo courtesy of FBI.

Photo courtesy of FBI.

Accused Boston bomber Dzhokhar Tsarnaev has told FBI investigators that he and his brother were operating alone and did not receive assistance from outside terrorist groups, officials said Tuesday.

A team of federal agents peppered the 19-year-old with questions about the Boston Marathon bombing plot on Monday shortly before a federal magistrate read the charges against him and gave him the Miranda warning informing him of his constitutional right against self-incrimination.

Tsarnaev remains in a Boston hospital, where his condition on Tuesday was upgraded to fair.

Read the full Los Angeles Times story.