Appearing on Sunday morning programs today, various officials stated that the suspected Boston bombers had made enough explosives to suggest they were planning more attacks. "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," Boston Police Commissioner Ed Davis told CBS' "Face the Nation." "That's my belief at this point."

"There were over 250 rounds of extended ammunition that was found at the scene. This was a five- to 10-minute gun battle that occurred there, punctuated by loud explosions," he added, saying that the explosive devices were homemade.

Governor Deval Patrick said on NBC’s “Meet the Press’’ that surveillance video showed Dzhokhar Tsarnaev dropping a backpack and walking away before the second bomb exploded. "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."

Mayor Thomas M. Menino said on ABC’s “This Week" that officials are pretty certain that brothers Dzhokhar and Tamerlan Tsarnaev acted alone in carrying out their plan: “All of the information I have is they acted alone, these two individuals, the brothers,’’ he said. “The older brother’s dead now. We have the second one...in very serious condition."

Regarding Dzhokhar's current condition, Menino added: “We don’t know if we’ll ever be able to question the individual.” He is currently listed as serious but stable at Beth Israel Deaconess Medical Center. CBS reports that he has a bullet wound in the back of his neck and another to his leg. And now investigators speculate that Dzhokhar tried to kill himself while hiding in a boat before being arrested by police during the backyard shootout in Watertown Friday evening.

The injury “had the appearance of a close range, self-inflicted style,” a senior law enforcement official told the Times. “He’s not in good shape.”