Sen. Luis Fernando Velasco's life began to unravel in 2008 when a lawyer appeared before prosecutors and accused him of conspiring with leftist rebels to coerce voters to support him.

His good name tarnished, Velasco was forced to temporarily abandon his Senate seat and was behind bars when his father suffered a heart attack. After four months in jail, prosecutors determined it was all a set up and his accusers had been paid by his political enemies to testify against him. Velasco was set free, and the lawyer and his accusers were arrested.

The senator's ordeal highlights a spreading problem undermining trust in Colombia's criminal justice system: professional liars paid and often groomed by corrupt lawyers to testify in court. Authorities have taken to calling it the "cartel of false witnesses," with paid liars sometimes testifying in dozens of cases at a time, parading from courtroom to courtroom.

So entrenched is the problem, the country's chief prosecutor set up a special task force two years ago to comb over the evidence in 3,000 cases where perjury is suspected. So far, around 100 cases have been overturned.

The latest reversal took place this week, when Colombia's Supreme Court absolved TV anchor Angelica Ramirez after she spent three years in jail after her ex-husband, with the testimony of a demobilized guerrilla, falsely accused her of plotting terrorist acts with the rebels.

"The false witnesses are a cancer on the justice system," Ramirez told The Associated Press, recounting how she was abused by other prisoners. "My life was destroyed."

Concern about the integrity of Colombia's courts comes at a sensitive time for the government, which is trying to negotiate peace with leftist rebels. Key to the two-year-old talks is entrusting judges to ferret out the truth in thousands of killings, kidnappings and war crimes involving rebels as well as military units. If faith in the courts is lost, the peace process would be at risk.

"If a peace deal is reached, common criminals will try to present themselves as guerrillas to win benefits," said Luis Gustavo Moreno, author of a new book on the phenomenon called "The False Witness." ''How will they do it? By accusing politicians of being their bosses."

Legal experts trace the false-witness phenomenon to a previous peace accord that brought the surrender a decade ago of 30,000 paramilitary fighters. Under a 2005 legal framework for the demobilization deal, former combatants faced a maximum of eight years in jail for battlefield crimes. But sentences could be sharply reduced if they implicated higher-ups or officials, creating a strong incentive to provide false testimony.

Testimony by former combatants led prosecutors to open investigations into more than 100 congressmen for allegedly assisting the right-wing militias. Only about a third of those lawmakers were convicted.

The problem has now spread beyond politics, with false witnesses offering carefully prepared "eyewitness accounts" in domestic disputes and murder trials for anywhere between $2,000 and $20,000, depending on a client's ability to pay and the victim's profile, said Amanda Cetina, a member of the chief prosecutor's special unit.

"The natural place for recruitment (of false witnesses) is inside the jails," Cetina said.

While jailhouse confessions are considered unreliable in many countries, Colombian prosecutors attribute great value on the testimony of prison snitches because criminality is so widespread but few capos are ever punished. It is one of their few effective tools to get a conviction.

False witnesses are coached by lawyers, in some cases even taking acting classes so they don't misspeak on the stand, Moreno says.

"Witnesses learn to lie in court as if they were reciting a recipe book," he said.

Perhaps the best-known reversal because of perjury is that of politician Sigifredo Lopez. He was kidnapped in 2002, along with 11 other regional lawmakers, when rebels raided the state legislature in the city of Cali. Lopez was released in 2009, escaping the fate of his fellow captives who the government says were killed by the rebels.

But Lopez's freedom was short lived. Three years later, he was detained and accused by prosecutors of complicity with the rebels in the abduction and slaying of his colleagues.

"They paraded me before the world as if I were Colombia's worst criminal," Lopez said.

Prosecutors eventually withdrew the charges after the FBI concluded his voice didn't match the one heard in a video giving orders to rebels on how to storm the legislature. Four false witnesses were eventually charged in the case.

Still bitter, Lopez tried to get his political career back on track but failed last year to win election to the Senate.

He now heads the Foundation for the Defense of the Innocent, which helps defendants clear their names. The group is pushing for stiffer punishments for perjurers, including mandatory jail sentences equal to the length of time their victims would have gotten. Currently perjury is punishable by six to 12 years.

Velasco had more luck than Lopez in relaunching his political career after his ordeal, winning re-election in 2010.

At the time of the false accusations, he had been denouncing ties between paramilitaries and officials in former President Alvaro Uribe's government.

He was absolved when several demobilized guerrillas, under interrogation by the Supreme Court, confessed they had been recruited by a lawyer working with members of the military to frame Velasco. The lawyer was arrested in 2013 along with three others for the false testimony.

Velasco considers himself lucky compared to poor Colombians who don't have the resources to mount a defense.

"Not everyone has the chance to defend themselves like me," he said.

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Associated Press writers Cesar Garcia and Libardo Cardona contributed to this report

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Jacobo Garcia on Twitter: https://twitter.com/jacobogg