The computer tech told the detective that the letter he examined was composed on a certain type of computer and printed on a certain type of printer, but there is no way to determine either of those things by examining a printed page.
A spectrographic analysis of the ink on the page might possibly identify the manufacturer of the printer based on the chemical makeup of the ink, but that's as much information as could be obtained.
A spectrographic analysis of the ink on the page might possibly identify the manufacturer of the printer based on the chemical makeup of the ink, but that's as much information as could be obtained.