WASHINGTON (AP) -- Boston's police commissioner says investigators believe the suspects in the marathon bombing were likely planning other attacks.

Commissioner Ed Davis told CBS' Face the Nation on Sunday that authorities found an arsenal of homemade explosives following a gun battle between police and the suspects last week in Watertown, Mass.

Davis says authorities have reason to believe 19-year-old Dzhokhar Tsarnaev and 26-year-old brother Tamerlan were going to attack other individuals.

He says the scene of the gun battle was loaded with unexploded improvised explosive devices that actually we had to point out to the arriving officers and clear the area.

He said on Fox News Sunday authorities cannot be positive there aren't more explosives that haven't been found. But he says the people of Boston are safe.

Dzhokhar Tsarnaev remains in serious condition at a hospital under heavy guard. Davis says authorities have not been able to interrogate him yet. Tsarnaev was taken to the hospital Friday night after being pulled from a boat in a Watertown backyard. Tamerlan Tsarnaev died in a gun battle with police.

The twin bombings killed three people and wounded more than 180.

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