A slew of Worcester County drug cases will be retried after a judge ruled that “egregious” conduct in the form of secret recordings made by Massachusetts State Police tainted the cases and denied defendants’ their right to pursue “vital defenses” at trial.

This case represents a failure on the part of MSP on many levels,” Judge Christopher P. LoConto wrote in his 34-page ruling.

Members of the Massachusetts State Police violated criminal law by making secret recordings during a Fitchburg-area drug sweep, and later gave unreliable testimony about their conduct under oath, a judge ruled Monday.