They will probably now spend that day in prison. Teenage love has turned into an American nightmare of betrayal, jealousy and violent death.
The tale is so bizarre as to be scarcely believable. But if confessions they both have signed are true, Zamora and Graham face conviction for premeditated murder.
Their victim, according to police, was Adrianne Jones, a 16-year-old schoolmate of Graham and, like him, a member of the cross-country team. Last November the two had a brief fling. Exactly a month later, the body of Jones was found by a lake at Grand Prairie, a suburb of Fort Worth. She had been beaten, and then shot twice with a 9mm pistol.
In tight-knit and God-fearing suburban Texas the crime was a sensation, but a complete mystery. A young man at Mansfield, where Graham and Jones were at high school, was briefly arrested, but released for lack of evidence. As the months went by police lost hope, until last week the answer emerged more than 1,000 miles away.
Diane Zamora, now in her first term at the US Naval Academy in Annapolis, Maryland, took part in a tell-all session with her two room-mates, discussing the worst thing each had ever done. In her case, it gradually emerged, the answer was that she and her boyfriend had committed murder.
At first disbelieving, the room-mates none the less reported the episode to the Annapolis authorities. Scarcely less puzzled, the academy informed police departments around Fort Worth. The unsolved killing at Grand Prairie seemed to fit. Initially Zamora maintained she had made her story up, "to gain sympathy and attention", and in the absence of conclusive evidence she was sent home to Texas.
Then the police interrogated Graham, by now a first-year cadet at the no less blue-riband US Air Force Academy in Colorado Springs. At first he maintained the murder was a fiction, but after he failed a lie detector test, he confessed. He now awaits extradition from Colorado to Texas. His girlfriend is in jail, in lieu of a $250,000 (pounds 165,000) bond. And their crime, it is clear, is not one of headstrong teenage passion but of coldblooded, carefully plotted revenge.
According to Grand Prairie police, a remorseful, guilt-stricken Graham quickly told Zamora of his tryst with Jones. The fling, he said in his confession to police obtained by a Dallas newspaper, was an "unclean act" that soiled the "purity" of his long-standing relationship. And, Zamora is said to have insisted, the only way to expunge it was to remove every trace of it, "if you want to solve this problem, we have to make sure she doesn't exist".
And so they devised their plan. On the night of 3 December 1995, Graham arranged to meet Jones and came to collect her at her home in a pick-up truck, in which his girlfriend was hiding.
They drove to the deserted lake where the killing would take place. The original scheme was to sink Jones' body in the lake.
But when Zamora climbed down from the back of the truck and attacked her with a barbell, Jones escaped. Graham then pulled out a 9mm pistol and shot her.
The two accomplices left her body and fled. Police recovered the gun at Graham's parents' home.
With the evidence seemingly so clear-cut, Graham's hometown of Mansfield, and Crowley, where Zamora lived, are stunned. The couple's American-dream- come-true had featured in the local papers.
He was, in the words of his lawyer Dan Cogdell, a "straight-A, pick-of- the-litter kid, who had never done anything wrong in his life".
The reputation of Zamora, who appears to have been the driving force behind the crime, was scarcely less.
Graham's lawyer now says his client did not pull the trigger, and that his confession was co-erced. Such are the manoeuvrings in murder cases, especially in Texas, which seeks the death penalty more frequently than any state.
But they will impinge upon the question at the heart of the case. How, for one fleeting indiscretion, could one life have been taken, and two others, so promising, been ruined?Reuse content