Tsarnaev "offered to provide certain kinds of cooperation and assistance, in the course of plea negotiations," the document unsealed on Wednesday read, as quoted by the NBC News broadcaster.
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However, the authorities "consistently rejected" Tsarnaev's conditional offers, according to the broadcaster.
The Boston Marathon bombing on April 15, 2013, killed three people and injured hundreds of others. Dzhokhar and his older brother Tamerlan were found guilty of the attack. Tamerlan was killed by police while on the run on April 19 of the same year, while Dzhokhar was arrested the following day and sentenced to death by lethal injection in May 2015.