BY GONZALO GUILLEN AND GERARDO REYES
El Nuevo Herald

The executions of innocent civilians reported by the Colombian Army as ''guerrillas killed in combat'' are not the responsibility of a few ''rotten apples'' in the armed forces -- as the Colombian government says -- but a widespread systematic practice, a U.N. investigator said.

Philip Alston on Thursday asked Colombia to acknowledge and stop the executions, known as ''false positives.'' In military jargon, the word ''positive'' is used to refer to an operational success.

In his preliminary report, at the end of a 10-day visit, Alston cited as an example of the nonjudicial executions the case of a young soldier killed while he was on medical leave and whose case was published last week in a three-part series in El Nuevo Herald and The Miami Herald.

Alston said he did not find any evidence that the executions were carried out as an official government policy or with the knowledge of President Alvaro Uribe.

According to Alston, the number of cases, their occurrence in different geographic zones, and the diversity of the military units involved, indicate that the executions were carried out in a more-or-less systematic manner by a significant number of Army elements.''

The Colombian Attorney General's Office is investigating the deaths of more than 1,800 people who were executed and presented as guerrillas killed in combat. More than a thousand servicemen have been implicated in the investigation.

Alston said he does not rule out that some of the victims were guerrillas, but said that the government has not given him any proof of that ``other than emphatic assertions.''

''The evidence that shows victims wearing newly ironed camouflage garments or wearing field boots four sizes bigger than their feet, or left-handed individuals holding a pistol in their right hand . . . negate even more the suggestion that they were guerrillas killed in combat,'' Alston said.

He added that ''among the dangerous guerrillas'' killed by the Army there were ''16- and 17-year-old adolescents, a young man with the mental capacity of a 9-year-old'' and ``a devoted head of family whose two brothers-in-law are in active military service.''

Alston expressed concern over what he called the ''systematic harassment'' of the servicemen toward the families of the victims and cited the case of the death of a young man in Soacha, south of Bogotá, who was making efforts to clarify and denounce the execution of his brother, whom the Army reported as a guerrilla killed in action.

Last November, the execution of a dozen residents of Soacha, buried as anonymous guerrillas, launched the scandal of the ``false positives.''

Some of the victims had been dressed in guerrilla uniforms. Firearms, munitions and grenades had been placed by their sides.

Those executions created the perception that this was a phenomenon limited to Soacha, Alston said.

Alston acknowledged that the government has taken ''important measures'' to stop the killings, among them disciplinary sanctions, better cooperation with the United Nations, a stronger supervision of the payments made to informers, the demand that combat casualties be investigated first by the judicial police, and a modification in the criteria for rewards.

Even so, the investigator said, ''the number of successful indictments continues to be very low'' and there continues to be ''a very worrisome gap'' between ''the actual practice and the official policies'' that condemn this kind of crime.