(Adds context, paragraph 5 and 9)
By Hugh Bronstein
BOGOTA, June 18 (Reuters) - A U.N. investigator criticized the Colombian army on Thursday for not rooting out the widespread practice among its troops of killing innocent civilians and making them look like guerrilla casualties.
The case of 19 men and boys shot dead by soldiers last year in the Bogota suburb of Soacha and then passed off as rebels killed in combat is but the "tip of the iceberg", U.N. rapporteur on extrajudicial executions Philip Alston said.
Colombians were shocked by the slayings by troops seeking promotions, bonuses and other benefits offered by an army under increasing pressure to crush the country's 45-year-old leftist insurgency.
The U.N. official, concluding a 10-day fact-finding mission, said such cases marked "a more or less systematic" practice by "significant elements within the military."
Alston said the practice was never an official state policy and the defense ministry has acted to end such killings. But efforts to bring the guilty to justice have been slow and inadequately funded, he added.
Civilians have been cut down by rogue soldiers around the country in what Alston called the "cold-blooded, premeditated murder of innocent civilians for profit."
The highest number of such murders were in the impoverished suburb of Soacha, where recruiters lured their victims with promises of lucrative jobs. Instead they were slain, then dressed as rebel fighters and photographed holding weapons.
"Evidence showing victims dressed in camouflage outfits which are neatly pressed, or wearing clean jungle boots four sizes too big for them, or left-handers holding guns in their right hands, or men with a single shot through the back of their necks, undermines the suggestion that these were guerrillas killed in combat," Alston said.
The government, which invited the fact-finding mission and cooperated with the inquiry, has taken "important steps to stop and respond to these killings," Alston said.
"But the number of successful prosecutions remains very low," he added.
President Alvaro Uribe, first elected in 2002, has used billions of dollars in U.S. aid to intensify Colombia's fight against cocaine-funded FARC guerrillas, making wide areas of the country safer.
Critics meanwhile denounced the Colombian army's "body count mentality" in which advancement through the ranks depended on delivering enemy corpses.
"All forms of incentives to members of the military for killing should be removed," Alston said. "The problem of impunity for past killings must still be addressed." (Reporting by Hugh Bronstein, editing by Anthony Boadle)