'Boston suspects had other plans'

Boston Police Commissioner Ed Davis told CBS's Face the Nation television program on Sunday that he believed the Boston Marathon bombers had plans to conduct further attacks.

Dzhokhar Tsarnaev, 19, is being treated in a Boston hospital after being taken into custody late Friday. He remains in serious condition. His 26-year-old brother, Tamerlan, died following a shootout with police overnight on Thursday.

'More attacks planned'

Davis pointed to the arsenal of homemade explosives found at the scene of a Thursday night shootout with police as reason to believe the bombers had more attacks planned.

"We have reason to believe, based upon the evidence that was found at that scene - the explosions, the explosive ordnance that was unexploded and the firepower that they had - that they were going to attack other individuals," Davis said, according to the Associated Press.

Police found unexploded devices on the street following Thursday's shootout, as well as one in the Mercedes that the brothers had carjacked earlier that day. The devices contained the same type of shrapnel used in the marathon bombs.

Talking to the suspect

Investigators are eager to question the surviving suspect, Dzhokhar Tsarnaev, but it remains unclear when or whether they will be able to do so.

Thus far, the suspect has been unable to speak owing to injuries to his neck and tongue, which he sustained while on the run from police, officials said.

There was also no indication when the young man would be charged or what exact charges he would face. One possible charge available to federal prosecutors would be the use of a weapon of mass destruction to murder.

US officials said on Saturday that they had assembled a special interrogation team to question Tsarnaev and planned to do so without reading him his Miranda warning, which guarantees suspects the right to remain silent and the right to an attorney.

The exception is allowed on a limited basis to help ensure public safety, such as instances where bombs may be planted.

Motive remains a mystery

Officials are still looking into possible motives for the attacks.

Tamerlan Tsarnaev studied accounting part time at Bunker Hill Community College in Boston between 2006 and 2008, and his brother, Dzhokhar, was a student at the University of Massachusetts-Dartmouth.

The brothers come from a Chechen community in largely Muslim Kyrgyzstan. The family moved to Dagestan in 2001, which is a republic of Russia in the North Caucasus region and home to a violent Islamist insurgency.

Neither of the Tsarnaevs were on federal watch lists, but the FBI did interview Tamerlan in 2011 after Russia told US officials that Tamerlan was a follower of radical Islam.

Whatever the motive, the brothers are suspected to be responsible for the worst terrorist attack on US soil since September 11, 2001. They are believed to have detonated two bombs near the finish line of the Boston Marathon last Monday, killing three and injuring more than 180 people.

tm/slk (AP, Reuters)