Mr. Calderón’s aides had long asserted that most drug war victims were involved in the trade or other criminal enterprises, judging by the earmarks of heavy weapons used or crime-ridden areas where they were found.

But victims’ advocates note that many bodies, some dug up from common graves after perhaps years, remain unclaimed and unidentified, leaving the circumstances of their deaths a mystery. In addition to the known killings, some 25,000 people have been reported missing in the past six years. How many fell victim to violence is unknown.

A new law, stalled during Mr. Calderón’s term but enacted a little more than a month after Mr. Peña Nieto took office on Dec. 1, aims to compile a more precise registry of crime victims and provide financial relief for their survivors, though critics contend the law does not clearly address who exactly a victim is or how the fund will be paid for.

The law and the memorial grew out of the emerging victims’ rights movement, but reflect also the uncertainties of assigning guilt and innocence.

In this case, said Luis Vázquez, a scholar at the Latin American School of Social Sciences in Mexico City, the split is between the middle and upper classes, which are concerned about crimes like kidnapping and extortion, and human rights groups, which are focused on abuses of the military and the police in the warlike attack on cartels.

“There are two groups and two discussions going on related to victims of crime,” he said.

It follows that those two sides disagree on whom the memorial should honor. They even dispute who came up with the idea for it.

Javier Sicilia, a poet embraced by the left whose son was murdered by a drug gang in the south-central city of Cuernavaca in 2011, said he first proposed a memorial for drug-war victims at a security forum in November 2011 with Mr. Calderón.