Documents the employee produced and the company relies on: commissioning procedures, configuration files, diagnostic guides, training material, and service records showing which machines he brought online. Add training records, performance history and any evidence of attempts to train a replacement, together with the payroll proving the qualifying year.
Gather artefacts before writing prose
Assemble the material first and let the petition describe what it shows, rather than writing a persuasive letter and hunting for support. Print the document headers with dates and authorship. Pull the service database for the machines he commissioned. Collect the internal training decks he prepared for the subsidiary's staff, and any correspondence in which a customer asked for him specifically because of the system involved. Where the company keeps nothing in writing, which is common in small manufacturers, begin recording now and describe the position accurately as it stands, since fabricating a paper trail is far worse than a thin one. A modest but genuine record, explained plainly, is a defensible petition.
Hypothetical example: an automated-hatchery sensor architect has extensive knowledge but most instructions are stored in a private repository. A first review preserves dated extracts, authorship logs, restricted-access policies and a plain explanation of what the code controls. The record should show both the special know-how and the U.S. assignment that needs it. Screenshots without context are weak; pair them with a manager’s declaration and project documents. Never manufacture a trail after the fact, because ordinary records with honest limitations are safer than documents that appear created for a petition.