Dzhokhar Tsarnaev reportedly told U.S. authorities that the motives for the Boston Marathon bombings were the U.S. wars in Iraq and Afghanistan.

His striking confession comes after he was charged for the horrific bombing. (Read Full Transcript of the Bedside Court Hearing.)

Tsarnaev, 19, who together with his older brother Tamerlan Tsarnaev planned the bombings that killed 3 innocent people and injured more than 170, reportedly denied that he and his brother received support from a foreign terrorist organization, the Washington Post reports, citing law enforcement officials.

Authorities believe that the two of them were "self-radicalized" through Internet sites and the wars in Iraq and Afghanistan, according to the paper.

"These are persons operating inside the United States without a nexus" to an overseas group, a U.S. intelligence official told the Post.

More details surfaced on Tuesday about the events that occurred on Friday when authorities confronted the two Tsarnaev brothers in the streets of Watertown, MA.

It emerged on Tuesday that Sean Collier, the MIT police officer that was killed by the two bombing suspects, was apparently lured into an ambush and shot death in order to steal his gun.

CBS News reports that Collier was shot in the head "execution style."

A few hours later, the older brother, Tamerlan, was killed in a shooting with police in Watertown, MA. The younger brother Dzhokhar, escaped but was later found hiding in a boat in the backyard of a residence in the same neighborhood.

Dzhokhar was charged Monday in his hospital room with using and conspiring to use a weapon of mass destruction. He was accused of setting off bombs in pressure cookers that killed three and injured nearly 200 people at the Boston Marathon finish line on April 15.

Dzhokhar was next face an indictment, where he could be faced with new charges by federal persecutors. He will likely be charged with the murder of MIT police officer Sean Collier who was killed Thursday night by one of the suspects.

After he is indicted in the bombing, he will face an arraignment in federal court and be asked to enter a plea. Someone charged with the crime with using a weapon of mass destruction will face the death penalty.