The deadly Boston Marathon bombing that killed three and injured more than 170 could have been the first of many attacks, according to Boston Police Commissioner Edward Davis.

Davis announced that authorities now believe the two suspects, Tamerlan Tsarnaev 26, and Dzokhar Tsarnaev, 19, allegedly responsible for Monday’s bombing, had been preparing and arming themselves for “further attacks,” The Telegraph reported Monday.

“It’s my belief that they were already manufacturing explosive devices. Further violent acts were inevitable,” said Davis.

While FBI has begun questioning Dzokhar Tsarnaev. Edward Deveau, the police chief of Watertown, Mass. -- where the brothers were apprehended -- said he believes the pair were working alone.

“I believe it is limited to the two brothers. As far as this little cell, this little group, goes. I think we got our guys,” said Deveau.

Deveau said the stolen Mercedes that the brothers used Friday to evade local police contained six improvised explosive device, a satchel bomb, handguns, a rifle, home-made grenades and 250 rounds of ammunition.

The Independent reported Monday that agents have begun questioning Tsarnaev. Officials are looking to determine if the brothers placed bombs at any other locations and if they were working with accomplices.

Due to what is believed to be a self-inflicted neck wound, Tsarnaev is communicating with officials in writing. Boston Mayor Tom Menino stated that due to the 19-year-old’s injuries, he may never be able to verbally communicate with officers.

Sunday evening, Tsarnaev’s condition has been downgraded from serious condition to critical but stable. He is currently recovering at Beth Israel Deaconess Medical Center in Boston.

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