WASHINGTON — Boston’s police commissioner said the lone surviving suspect in the Boston Marathon bombing is in serious condition and authorities have not been able to try to interrogate him.

Commissioner Edward Davis also told CBS’ “Face the Nation” that the crime scene from the early Friday firefight in Watertown, Mass., was “littered” with unexploded improvised explosive devices.

Davis said it’s his belief that 19-year-old Dzhokhar Tsarnaev and his 26-year-old brother Tamerlan “were going to attack other individuals” – and Davis says that’s based on the evidence at the scene and the firepower that the brothers had.

Tamerlan died in the gunbattle with police in Watertown.

Davis says “this was as dangerous as it gets in urban policing.”