As a Republican congressman from Arkansas, Jay Dickey, through an obscure amendment, single-handedly prevented the federal government from investigating the public health effects of firearms-inflicted violence for the last two decades.

The legislation, a rider he attached to a House bill in 1996, stripped $2.6 million from the Centers for Disease Control and Prevention — the precise amount budgeted for a study of the health effects of shootings.

His amendment also stipulated that “none of the funds made available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control.” That provision has dissuaded the agency from delving into the issue since then.

But in 2012, long after he left Congress and right after a gunman killed 12 people and injured scores more in an Aurora, Colo., movie theater, Mr. Dickey, who died on Thursday at 77, did an about-face. He declared that research could have been conducted without encroaching on the rights of legitimate gun owners.