Key Identification, Decoding, and Impressioning Evidence
Domain 6 tests key identification, decoding, and impressioning evidence: reading a key's geometry, relating it to a lock, and recognizing the traces left when a key is made or altered.
Identification and decoding
- Record bow markings, blade profile, keyway, warding, shoulder, tip, and number of cuts. A key gauge or calipers measure spacing, root to root, and depth from the bottom of the blade or root.
- Decode cuts from shoulder to tip, using the lock manufacturer's spacing and depth increments. Check MACS, the maximum adjacent cut specification, when evaluating whether a cut key could operate a given cylinder.
- Distinguish original, duplicate, and master keys. A master key may have extra cuts or a different depth sequence; do not assume the highest cut is the operating cut.
- Impressioning evidence includes a blank with clamp or vise marks, file cuts, and pressure marks at pin positions. The pattern of marks can show which pins bound first.
Worked example
A five-pin key is measured with spacing of 0.156 inch and depths in four increments. The cuts decode as 3-5-2-4-1. The lock's keyway and spacing match the same family, but the sixth position is a zero cut with a wear scar. You report the decoded bitting with the measurement method and note the wear uncertainty; you do not claim the key is original.
Traps
- Measuring a worn key and treating the result as factory bitting.
- Decoding from tip to shoulder when the system is shoulder-referenced.
- Ignoring MACS or master-key hierarchy.
- Assuming bow stamping proves manufacturer or model.
- Calling file marks 'impressioning' when they are ordinary duplication burrs.