Dalton began skipping his school classes following his return to Lafayette. In March 1972, he was committed to the Louisiana Training Institute for truancy at the insistence of his mother. Released only seven months later, he soon came into conflict with the authorities on charges of burglary, theft, and "false firearms". In March 1974, he was committed to the Lafayette Juvenile Youth Authority, a residential program for delinquents. He ran away from that facility after a month; upon his return his commitment was terminated and he was released on probation to his mother.
In June 1974, Dalton was arrested for the killing of John Doucet, a taxi driver. Dalton admitted the killing and was committed once again to the Louisiana Training Institute. In a later statement about the incident Dalton stated that he and two friends called a cab with the intention of robbing the driver. One of his companions was carrying a gun. The three directed the driver to a quiet part of town and persuaded him to stop while they searched for an address. Dalton insisted on taking the gun from his companion because the other youth appeared to be nervous. Dalton approached the driver, and believing that the driver was reaching for a gun of his own, fired twice and began running. While fleeing he told a passerby to call an ambulance because someone had been shot. Dalton later turned himself in to the police and admitted that he had killed the driver.
A psychiatric evaluation of Dalton was performed in 1974. He was found to be intellectually limited and to have very poor judgment. Dalton was diagnosed as having borderline mental retardation, and it was questionable if he knew the difference between right and wrong. He considered the boy to be “a definite danger to himself and others, and his dream content suggests that it is a matter of accident that the cab driver was killed rather than the boy being killed. He is equally likely to get himself killed in the near future.” The psychiatrist therefore recommended a lengthy confinement, followed by transfer to permanent facilities. The juvenile courts had jurisdiction over the defendant until he was twenty-one. The doctor’s recommendation would have served to keep the defendant confined until December, 1980.
In 1976, however, another doctor conducted a psychiatric evaluation of the defendant and recommended that he be discharged. He concluded that the defendant's values had changed, but cautioned that "suitable conditions (should be) imposed to be sure he had adequate supervision and is going to live in a fairly stable environment". That doctor also suggested that fairly rigid probation requirements be imposed. On December 10, 1976, Prejean was released to the custody of his aunt in Houston, apparently without any probation requirements. Within seven months, Dalton was once more under arrest for killing a human being.
At about five o'clock in the morning of July 2, 1977, Prejean, his brother Joseph, Michael George, and Michael Broussard left Roger's Nite Club in Lafayette Parish. The four had spent the night drinking in various lounges in the vicinity. They left Roger's Nite Club in a 1966 Chevrolet driven by Dalton, with his brother in the front seat and the other two in the back. The car's taillights were not working, and within a few hundred feet of the lounge, Trooper Cleveland, who was on his way to work driving his police vehicle, signaled the Chevrolet to stop. Prejan and his brother attempted to switch places in the front seat because the defendant had been driving without a license. The trooper noticed the switch and ordered the occupants out of the car. He told Michael George and Michael Broussard to get back in, however, and began to search Joseph Prejean. Dalton Prejean, back in the car, stated in reaction to the trooper's pushing Joseph against the car, over Joseph's protest, “I don't like the way he's doing my brother.” Dalton then took a .38 caliber revolver from under the car seat, got out of the car and approached the officer with the gun hidden against his leg. As he neared the trooper he fired without warning. Trooper Cleveland was struck by two bullets and was killed. Dalton and his companions fled the scene but were apprehended several hours later.
Dalton was once again given psychological tests during pretrial confinement. On the basis of the Wechsler Intelligence Scale, the Stanford Binet Vocabulary Subtest and the Bender-Gestalt Test, Dr. William Hawkins determined that he functioned at the dull normal level in the verbal area but in the borderline mental retardate area in the performance area. He had a verbal I.Q. of 82 and a performance I.Q. of 72. His full scale I.Q. is 76, with a full scale mental age of thirteen years and six months.
Dalton Prejean was charged by grand jury indictment with first degree murder in violation of Louisiana Revised Statute 14:30. The trial was transferred from Lafayette Parish to Ouachita Parish because of pretrial publicity. After a three day bifurcated trial beginning on May 1, 1978, a jury of twelve persons found the defendant guilty as charged and unanimously recommended that the death penalty be imposed.
The death penalty appeal reached the US Supreme Court in 1990; in November 1989 it had granted a stay on the eve of his scheduled execution. On April 17, 1990, the Court lifted the stay without comment. The case received international attention; the European Parliament called for commutation of the sentence and a review of the evidence.
His final statement was:
State v. Prejean, 379 So.2d 240 (La., 1979.)