developing latent prints (forensics q3)

latent prints: invisible prints caused by the transfer of body perspiration or oils present on the finger to the surface of an object

dusting

• appropriate surface

  • ridged/non-porous

    • glass, plastic, metal

• theory

  • dust will adhere to sweat and oils left behind

  • cover surface with dust

  • remove excess dust

    • brush or blow

  • use tape to lift the print

  • place print on a card

iodine fuming

• appropriate surface

  • porous and non-porous

    • paper, index cards, magazines, and cardboard

• theory

  • sweat and oil will absorb iodine vapors

  • place object in an enclosed container with iodine crystals

  • print should develop in a few minutes

ninhydrin

• appropriate surface

  • porous

    • paper, tissue, clothing

• theory

  • ninhydrin reacts with amino acids to form a purple compound 

  • soak suspected surface with ninhydrin solution and allow to dry

  • print should develop within 24 hours

silver nitrate & uv-light

• appropriate surface

  • porous

    • paper, drywall

• theory

  • when exposed to uv light, silver nitrate reacts with salt in sweat to form a blackish-brown compound

  • spray surface with silver nitrate solution

  • expose to uv light

  • print should develop in 5-10 minutes