While colleagues were suspicious of her shoddy work habits and unusually high output and reported concerns to supervisors, little action was taken for more than a year, according to the police inquiry.

A one-page overview of the lab’s routine procedures, provided to the Globe from someone familiar with its operations before it was closed in August, indicates that a primary chemist is assigned a sample from the lab’s evidence room, weighs it, and performs testing to preliminarily identify it. That person then prepares vials of the substance to send to a secondary chemist, known as the lab’s GC/MS person, who analyzes the vials in a machine to confirm the identification.

That process, known as gas chromatography–mass spectrometry, first separates drug samples into their component parts. For instance, it separates cocaine from the baking powder, laxatives, or other substances drug dealers typically cut the drug with to inflate its weight. Next, the machine analyzes the chemicals and prints out a characteristic pattern, similar to a bar code, that is used to identify a sample. For instance, it compares the pattern for the sample of presumed cocaine being tested to the pattern of a known sample of cocaine.

The GC/MS chemist analyzes the printout and records the results on a control sheet, which is initialed by that chemist and the primary chemist on the case, and then the primary chemist returns the original samples and all documentation to an evidence officer.

“The GC/MS [machine] produces a printed, recorded analysis of the sample, but unless you are highly trained you may not be able to know if it’s traceable to a specific sample of evidence,” said Justin McShane, a Pennsylvania criminal defense attorney and senior instructor in gas chromatography-mass spectrometry at the American Chemical Society, a trade group of more than 164,000 chemists.

Because of the complexity, and lack of cameras recording the preliminary tests, McShane said, it is possible for an unscrupulous chemist to dupe colleagues and prosecutors and defense lawyers, who depend on the work but are rarely given more than a simple card that indicates whether the evidence was positive or negative for ­illicit drugs.

McShane said he routinely hears “horror stories” from chemists he trains about unrelenting pressure to test more samples. Dookhan allegedly confessed to State Police that she forged colleagues’ initials and contaminated samples to “get more work done,” according to their report.