BOSTON MAYOR: Information Suggests Bombing Suspects Acted Alone

"All of the information that I have they acted alone," Thomas Menino said during an appearance on ABC's "This Week with George Stephanopoulos" Sunday.

However, he added that it was not clear if they would be able to question the suspects about the possibility of outside help.

"The older brother's dead now. We have the second one at Beth Israel Hospital in very serious condition," he said "And we don't know if we'll ever be able to question the individual."

So far the FBI has only named two people in relation to the attack. Both suspects, Dzhokhar and Tamerlan Tsarnaev, had family ties to Chechnya, an area of Russia known for Islamic insurgency. The older suspect, Tamerlan, took a six-month-long trip to nearby Dagestan last year that is being investigated.

However, no other groups or individuals have been linked to Monday's bombing. A website affiliated with rebels from the North Caucasus region has disavowed the attack with a note saying "Caucasus fighters are not waging any military activities against the United States of America."

Menino said that another individual was taken into custody after the discovery of a pipe bomb, but this was not related to Monday's bombing.