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Lawyers for the Boston Marathon bomb suspect on Tuesday renewed their request to delay the start of the trial — now scheduled to begin Jan. 5 with jury selection — until September 2015.

Dzhokhar Tsarnaev's attorneys say they've been overwhelmed with material from prosecutors, are finding it difficult to research Tsarnaev's family overseas, and are worried that the jury could end up deliberating around the second anniversary of the blast that killed three and injured more than 260.

"Given the ubiquity and intensity of anniversary news coverage and related public activities, even the most conscientious jurors are likely to be exposed to influences that would require a mistrial," defense lawyers wrote in a motion filed in federal court.

"This risk could be avoided — and the fairness of the trial increased — by waiting to begin trial until after the anniversary has passed."

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The government's witness list contains the names of 590 law enforcement personnel and 142 civilian witnesses, and prosecutors say they might use any of 1,238 exhibits. Some of the material turned over was not indexed, making it difficult to sort through the mountain of data, they complained.

"The sheer volume of material, alone, requires a continuance. As a practical matter, it impossible for the defense to digest this information, much less attempt to pursue investigative leads it may suggest, in time to make effective use of it at trial," Tsarnaev's lawyers argued.

They noted that the paperwork they received days ago suggest the government is still analyzing some of the physical evidence, including components of the bombs' triggering apparatus — a transmitter recovered from Watertown, where Tsarnaev was eventually captured, and the explosion site.

Starting the trial in January, they argue, would be unusually fast given that prosecutors are seeking the death penalty against Tsarnaev.

"The trial in this case is currently set to begin just 18 months after the defendant was indicted, which would bring this case to trial faster than 99 of the 119 federal capital trials to get under way since 2004," they wrote.

The defense also said it has encountered "new obstacles" in digging into Tsarnaev's family history in Chechnya, Dagestan and Central Asia and aren't sure they can get get witnesses they have identified to show up at the trial.

The judge has declined in the past to push the start of the trial into late 2015. He did grant a small delay from November 2014 to January 2015.

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