A new report by Human Rights Watch offers an extensive and blistering review of investigative and prosecutorial abuses in American terrorism investigations.

Of special concern is the extensively documented use of informants by the FBI to target Muslim centers and mosques without specific evidence of wrongdoing. The report describes extensive involvement by informants in recruitment, planning, and execution of terrorist actions that seems to border on entrapment.

Human Rights Watch concluded that half of the 500 counter-terrorism convictions since 9/​11 used informants, and 30 percent of those were sting operations in which informants played an active role.

Such tactics are not new to law enforcement, but some details are disturbing: Informants targeted people with certain political and religious beliefs without suspicion of criminal wrongdoing. They targeted people with clear mental and intellectual disabilities. They would rebuff suspects’ initial reluctance and spend years in recruiting, or offer vast sums of money to persuade them.

Often, these were not criminal masterminds. A judge described one offender: “Only the government could have made a terrorist out of Mr. Cromitie, whose buffoonery is positively Shakespearean in scope.” The trials were often complicated by reliance on classified evidence, which is difficult to challenge. Even worse, some cases included interrogations of suspects by foreign governments that likely involved torture.

Since the Sept. 11, 2001, attacks, law enforcement has understandably shifted its attention to ferreting out terrorist plots, abroad and at home. But this turn should not come at the expense of constitutionally guaranteed civil liberties.

First Published July 26, 2014, 4:00 a.m.