One day last December, a Brooklyn prosecutor called the Police Department laboratory to check on a test of drugs that had been seized six weeks earlier.

The drugs were nowhere to be found in the laboratory.

As officials hunted for the evidence in that case, they made a startling discovery: The drugs seized in 42 other arrests made in Brooklyn that same day, Oct. 20, 2006, also had vanished without a trace.

In short, all the evidence from every narcotics arrest in Brooklyn that day was gone.

“A search was conducted, disclosing that an entire bundle of narcotics, 43 in total, which should have been submitted to the laboratory for examination was not present,” Dr. Peter Pizzola, the director of the laboratory, wrote in a letter in April to an organization that oversees forensic laboratories. “Additionally, all paperwork associated with this delivery was also missing.”

Despite an inquiry that began over a year ago, officials still cannot say whether the drugs were lost, stolen or thrown away. Investigators believe that a police officer serving as a courier took several large plastic bags of drugs as far as the laboratory. There, the trail goes cold.