Law enforcement sources said the 20-year-old suspect was under guard at an undisclosed Boston hospital.
Fox News reported that the suspect suffered severe burns.
It was not immediately clear why the man was hospitalized and whether he was injured in the attack or in his apprehension.
The man was caught less than two hours after the 2:50 p.m. bombing on the finish line of the race, in the heart of Boston.
In addition, Boston police have surveillance video of someone bringing multiple backpacks to the blast site, according to CBS News. (Continues)