Students hand picked by Dolores Umbridge for their support of the Ministry against Dumbledore (and specifically were willing to support Umbridge) were formed into a group called the Inquisitorial Squad. The members seemed to all be Slytherins.
They were given the authority to open and inspect packages, tell on people to Umbridge, and do other such dirty work for her. The members of the Inquisitorial Squad participated in the raid on the Dumbledore's Army (DA) meeting and captured a number of DA members, including Harry. Members of the Inquisitorial Squad were a small silver letter I on their robes. Although Prefects are not normally allowed to take points away from fellow prefects, members of the Inquisitorial Squad could and did.
- Draco Malfoy
- Vincent Crabbe
- Gregory Goyle
- Pansy Parkinson
- Millicent Bulstrode
- an unidentified sixth year girl
After the Weasley twins left Hogwarts, the Inquisitorial Squad members were attacked in clever ways. Warrington developed a skin condition that made him look like he was covered in in cornflakes and Pansy Parkinson grew antlers (OP29).