Latest polls indicate that a serious issue might prevent Juan Manuel Santos, the former defence minister and candidate of the ruling U party, from winning the Colombian presidency.

Here the issue is known as the "false positives" scandal - the army's extrajudicial killing of civilians who are later presented as guerrillas to increase the battle body count.

Soldiers and officers were offered vacations, promotions and trips abroad as a reward in exchange for results.

"Efficiency was measured with the amount of dead guerrillas. There was a perverse logic behind it. You cannot measure success like that," said Mauricio Garcia Duran, who is from a human rights group in Bogota.

Practice continuing

Rights groups say there have been around 2,000 cases of false positives in Colombia. And while the number of deaths has been falling dramatically, the practice is continuing, with 17 people killed last year, according to the Centre for Investigation and Popular Education (CINEP).

What is worse is that most of those killed were poor young men and women, desperate to find work, so they did not hesitate when an opportunity came up.

I met with Luz Edilia Palacio Bustamante in the town of Soacha, just outside Bogota. It was here where the scandal first broke. She says that men were recruiting young men to work outside their hometowns.

"My son was about to have a baby," she says. "So he needed money to take care of it. He saw a chance to make some money so he left."

These men and women were later found dead in mass graves and the army claimed they were guerrillas. In fact, there have been reports that they were dressed up to look like guerillas before being killed.

"My son was not a guerrilla," she told me. "These recruiters were paid by the military to find possible victims so that they could kill them later on. Each victim was worth for the recruiters about $300."

The opposition says Santos benefitted from this directive as the amount of killings sharply increased while he was minister of defense.

Crimes against humanity?

Since the 1960s, Colombia has been battling against left wing guerrillas. Uribe's tough stance against them has turned him into one of the country's most popular presidents, but some believe his push to obtain results may have turned into an incentive to commit murder.

Rafael Pardo, who is also a former defence minister and presidential candidate, said "we saw some cases of false positives in the past", but "what has happened in this government is that there has been a systematic killing of civilians - there is no precedent in our history".

"This is a crime against humanity," he told me.

Many human rights groups are worried about what would happen if Santos becomes president. Felipe Lleras Zuleta, a renowned Colombian journalist , said that "somebody in the higher ranks has to pay - those deaths cannot go unaccounted for".

He is one of the many Colombians who would like to see Santos go before the International Criminal Court.

US ties

Colombia is a key US ally in the region and a recipient of US military aid. After the scandal, the US halted military aid to those units involved in the executions, but isn't it time to rethink America's policy in Colombia completely?

After all, many of these killings took place in order to produce results so that the US would continue giving money to fight drug trafficking and guerrillas who are involved in the drugs trade.

So far, there have several convictions and a serious restructuring within the army. But many accused have also been released because of legal wrangling and technicalities.

Uribe has vowed to make those responsible pay, but Santos has seemed untouchable. The future of that investigation, though, may rely on who becomes this country's next president.