BOSTON (AP) - The attorneys for Boston Marathon bombing suspect Dzhokhar Tsarnaev cannot take their own periodic photos of him, a judge ruled on Friday, denying the request pertaining to "his evolving mental and physical state" and whether his statements to authorities after his arrest were made voluntarily.

United States Magistrate Judge Marianne Bowler found Tsarnaev's lawyers could not take their own photos, saying the Fort Devens prison where Tsarnaev is housed, has a policy against visitors bringing cameras.

The motion from Tsarnaev's lawyers remained sealed on Friday. But in her ruling, Ms Bowler included excerpts from the defence filing which suggest Tsarnaev's lawyers may want to use the photos to argue for "sentence mitigation".

Tsarnaev, 19, is charged with using a weapon of mass destruction in the April 15 bombings. The two explosions near the finish line of the marathon killed three people and injured more than 260.

Ms Bowler said Tsarnaev's lawyers asked if they could regularly take their own photos of Tsarnaev.

"The defendant contends that his 'injuries over time' provide evidence of 'his evolving mental and physical state' which, in turn, is probative of 'the voluntariness of (his) statements and sentence mitigation argument'," Ms Bowler wrote.

Tsarnaev was badly wounded in a gun battle with police before his arrest. His lawyers could argue that statements he made to authorities after his arrest on April 19 were not voluntary because of his poor physical condition.

Ms Bowler said the Bureau of Prisons could take photos of Tsarnaev with his lawyers present but those pictures would have to be shared with prosecutors.