Pastrana's rival Serpa was stopped by guerrillas
When the guerrillas forced former culture minister Consuelo Araujo onto her knees and shot her twice in the head, they also killed the last vestiges of public faith in the country's peace process.
President Andres Pastrana, who described the act as "vile and cowardly", now finds himself in an impossible position. The public outcry after the murder of the popular former minister is deafening. Too deafening to ignore.
Yet after three years of talks there has been no tangible progress. Not only have the rebels refused to call a ceasefire, but they have escalated their attacks on isolated police stations across the country and brought kidnapping to record levels along with other types of extortion.
Now Mr Pastrana has been forced back to the drawing board.
"I've decided to evaluate the peace process in its entirety, component by component, with the certainty that Colombia's pain and its profound disgust for violence won't fall into a vacuum," he said in a televised address on Sunday.
Source of tension
The safe haven has been continual source of tension, brought to a head last weekend. The massive zone, granted for the purposes of peace, has been abused by the FARC. Critics allege that the guerrillas have used the area, where security forces are forbidden to enter, to build up military strength, recruit minors, import arms, export drugs and hold kidnap victims.
Last Saturday the Liberal Party presidential candidate, Horacio Serpa,
staged a march from Bogotá to the safe haven, aimed a highlighting guerrilla
abuses and pressuring the rebels into making real concessions in peace
negotiations.
On the outskirts of the zone - 200km south of the capital - he was stopped by armed guerrillas who said they had placed a car bomb and mines across the road and that Mr Serpa had to turn back.
Accompanied by hundreds of supporters and press, Mr Serpa insisted this was a defeat not for him but democracy, and the tensions over the safe haven flared again and the questions were asked: Was this a zone for peace, or a Marxist mini-state which the guerrillas were using to prosecute their war against a democratically-elected government?
The options facing President Pastrana are few and unappealing. He is under pressure not just from an outraged public but from the statements made by the presidential hopefuls, all of whom are hoping to capitalise on public frustration with the peace process.
Tough talk
They are talking tough knowing it is President Pastrana who has to make the decisions.
Even his own party has lost patience with the guerrillas.
"The FARC is demonstrating that they have no desire for peace," said Carlos Holguin Sardi, head of the ruling Conservative Party, from which Mr Pastrana comes.
But should the president bow to public demands to remove the guerrilla safe haven or take revenge in some way on the rebels, the last three years of negotiations will have been in vain and any hopes of a negotiated peace gone.
Yet he cannot afford to let the FARC get away unpunished for these latest atrocities or what little public support he still has will evaporate.
The stakes are higher than ever before. Peace seems more distant than it has in 37 years of fighting, and the results of an end to the peace process will be to plunge Colombia into all out civil war.