Which technique is best for developing latent fingerprints on plastic surfaces?

Developing latent fingerprints on plastic surfaces requires a technique that can effectively adhere to the unique characteristics of such materials. Magnetic powders are particularly advantageous for this purpose. They adhere well to the ridges and contours of latent prints, making them visible against the non-porous surfaces of plastics. The use of magnetic powders allows for precise application and can yield high-contrast results, especially when used on items like plastic bags or containers where the print may not be very pronounced.

In contrast, other techniques such as iodine fuming, silicone casting, and ninhydrin are more suited for different types of surfaces or conditions. Iodine fuming requires a porous surface to react with the oils in the fingerprint, while ninhydrin is effective for porous surfaces such as paper due to its ability to react with amino acids. Silicone casting is primarily a method for creating a mold of a fingerprint rather than a development technique for the latent print itself. Therefore, the selection of magnetic powders as the most effective technique for developing prints on plastic surfaces aligns with the specific interaction that occurs between the powder and the non-porous material.