BAHAWALPUR, Pakistan — Prof. Khalid Hameed’s devotion to teaching often led him to arrive early for work, and the day he was killed was no different.

Professor Hameed, a senior English lecturer at Government Sadiq Egerton College in the Pakistani city of Bahawalpur, parked at about 8 a.m. on March 20, signed the staff room register, unlocked his office and walked in. His killer came up from behind, hitting him in the head with a heavy padlock and stabbing him several times. Professor Hameed, 59, who was six months from retirement, died immediately.

One of his students, Khateeb Hussain, was detained by the police. In a video of his interrogation, Mr. Hussain said he killed Professor Hameed — a devout Muslim, according to his family — because he had insulted Islam. Six months later, no charges have been brought against Mr. Hussain, or against a preacher from Tehreek-e-Labbaik Pakistan, a hard-line Islamic group, who the police say incited him to kill.

The murder has devastated Professor Hameed’s family and chilled his colleagues at Sadiq Egerton College. They see it as a horrifying new chapter in a campaign against liberal education, which small but influential extremist groups in Pakistan consider unacceptable. Many of the teachers are now wary of speaking freely to their students.