The Tsarnaev brothers suspected in the deadly Boston Marathon bombings were carrying homemade bombs and grenades, which they lobbed at police when cornered, the city’s police commissioner said. He added that the suspects had planned further attacks.

"We have reason to believe, based upon the evidence that was found at that scene - the explosions, the explosive ordinance that was unexploded and the firepower that they had - that they were going to attack other individuals," Commissioner Edward Davis told CBS's Face the Nation on Sunday.

"That's my personal belief at this time," he continued.

He said that more than 250 spent rounds of ammunition were found at the scene, and that the ground was "littered with unexploded improvised explosive devices that we had to point out to the arriving officers".

Another device was found inside a vehicle the brothers had previously carjacked.

Speaking with Fox News Sunday in an earlier interview, Davis stated the suspects “had plans to use those explosives, possibly on soft targets."

The elder brother, 26-year old Tamerlan Tsarnaev, reportedly got within three meters of police officers involved in the shootout before he ran out of ammunition and was tackled. He later died from wounds sustained in the shootout on Thursday.

His injured younger brother, 19-year-old Dzhokhar Tsarnaev, fled the scene, forcing officers to conduct a house to house search in Watertown. He was arrested late on Friday when he was found seriously injured in the backyard of a private residence.   

A transport officer was left seriously wounded in the gun battle which fatally injured Tamerlan, while the brothers are also suspected of killing an MIT police officer on the same day.

Davis said tracing back all of the weapons used by the brothers would constitute a “significant part of the investigation.”

In a previous interview, Davis reiterated his confidence that the two individuals responsible for the bombing “are either dead or arrested at this point,” as authorities believe the brothers had no accomplices in the attacks.  

He further said Dzhokhar Tsarnaev, who was in “serious but stable condition” after suffering gunshot wounds to the leg and neck while being apprehended, was “in no condition to be interrogated at this point in time."

He is expected to be questioned without first having been read his Miranda rights – which grant him the right to an attorney and the right to remain silent – due to a rare public safety exception.

The Tsarnaev brothers

The High-Value Detainee Interrogation Group - a multi-security agency unit tasked with interrogating high-value suspects – is waiting at the Beth Israel Deaconess Medical Center in Boston, where Dzhokhar is convalescing under heavy guard.

However, Boston Mayor Tom Menino told ABC's This Week said that due the extent of Dzhokar’s injuries,“we don't know if we'll ever be able to question the individual." While the surviving suspect was expected to be charged over the weekend, prosecutors have not yet said what charges he would face. It has been speculated that the naturalized American could be charged with using a weapon of mass destruction to kill people.

The federal public defender's office in Massachusetts has already agreed to represent Dzhokhar once he is charged.

Meanwhile, Massachusetts Gov. Deval Patrick told NBC on Sunday that surveillance footage from the Boston Marathon bombing clearly put Dzhokhar at the scene of the attack.

"It does seem to be pretty clear that this suspect took the backpack off, put it down, did not react when the first explosion went off and then moved away from the backpack in time for the second explosion," Patrick said.

"It's pretty clear about his involvement and pretty chilling, frankly." Patrick added that he had not viewed all of the available video evidence, but had been briefed by law enforcement officials about it.

Investigators have determined the bombs were fashioned from pressure cookers packed with explosives, nails and ball bearings which were hidden in black backpacks.

Three people were killed and more than 180 injured when the two bombs exploded within 13 seconds of each other near the finish line of the Boston Marathon on Monday.

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