After joining the faculty at New Haven University, Li used the university's chemical analysis laboratory to help the police investigate criminal cases on numerous occasions. In 1979, the Connecticut state police hired Li outright as their senior forensics expert, and he then rose through a number of positions to become the head of the entire Connecticut state police force in July, 1989.
到了紐海文大學後，李昌鈺先毛遂自薦運用學校的化驗室協助康州警方破了多起案件，一九七九年康州警政廳遂聘請李昌鈺擔任首席刑事鑑識專家，之後又擢升他為康州刑事化驗室主任，八九年七月索性延攬他任康州警政廳長。