list of 500 items from secret prisons are on display this year . Exhibits include death masks of hanged criminals and bullet shrapnel . Syringe and poison Kray twins intended to use for witness intimidation . Masks worn by first offenders convicted for murder based on fingerprints . Gallstones of victim of John poisoning , known for dissolving people in acid . Personal possessions of Ronnie Biggs recovered from hideaway in 1963 .
Selection of 500 items from secret museum going on display this year . Exhibits include death masks of hanged criminals and bomb shrapnel . Syringe and poison Kray twins intended to use for witness intimidation . Masks worn by first criminals convicted for murder based on fingerprints . Gallstones of victim of John Haigh , known for dissolving people in acid . Personal possessions of Ronnie Biggs recovered from hideaway in 1963 .