CAIRO — Ever since the brutalized body of a 28-year-old Italian student, Giulio Regeni, was discovered on the side of a road on Feb. 2, lurid theories have abounded about who, or what, was responsible for his death.

Egyptian news media accounts, lawmakers and government officials have variously blamed an auto accident, sexual misadventure, drugs, espionage, a mystery assassin, the outlawed Muslim Brotherhood — everything, it seems, except the scenario that Washington, Rome and other European capitals think is most likely: that Mr. Regeni was abducted, gruesomely tortured and killed by an element of Egypt’s own security forces.

The case is still headline news in Egypt and Italy, and Western officials say the furor has crystallized their concerns about a much broader problem. They worry that escalating political repression and human rights abuses in Egypt are signs of weakness in President Abdel Fattah el-Sisi’s grip on power, potentially threatening the stability of a key Middle Eastern ally.

Reports of abductions, torture and brutality by Egypt’s security forces have surged in recent months, prompting debates in several Western countries about how to deal with Egypt. Secretary of State John Kerry met with senior State Department officials last week to consider the issue.