The FBI has mishandled large amounts of evidence in its offices across the United States, The New York Times reported Friday after reviewing an internal report from the investigative force.

The FBI has failed to keep close track of the weapons, valuables, money and drugs it keeps as part of its criminal cases, the report said, adding that almost half of the evidence reviewed by an internal investigation had errors.

The probe reviewed more than 41,000 pieces of evidence.

Mistakes in evidence collection pose a serious problem for the Federal Bureau of Investigation since errors can cause judges to toss out cases.

The FBI is notifying prosecutors of the report results and the risk of a mistrial.

Many errors were attributed to computer glitches, but the report also found instances of agents taking evidence from storage and not returning them for months. In several cases evidence has not been returned for years.