Despite the meritorious efforts of the doctors at Parkland Hospital, the wounds to President John F. Kennedy were deemed too severe to survive and his condition was, according to the Warren Report, "hopeless, and the extraordinary efforts of the doctors to save him could not help but to have been unavialing."
Admiral George G. Burkley, the President's physician, arrived at Parkland as emergency treatment was underway. Burkley is quoted as saying, "my direct services to him at that moment would have interfered with the action of the team which was in progress."
Shortly before 1 p.m., last rites were administered by Father Oscar L. Huber of Dallas' Holy Trinity Church. In a statement later published online by Baylor University††, Huber recalled the day in Dallas where he watched on television as the president's plane landed at Love Field. A short time later, Huber said he walked from the church to Lemmon and Regan streets to watch Kennedy's motorcade pass by. He recalled the "thrilling moment" as Kennedy and the first lady waved and smiled at onlookers as they headed toward downtown because, "I had never before seen a President of the United States."
A few minutes later, an assistant delivered the news to Huber that the president had been shot and was taken to Parkland Hospital, which, according to Huber, was in the confines of Holy Trinity parish. A call was then received at the church, from someone at Parkland, saying the first lady had requested a priest to tend to the spiritual needs of her husband. Huber and Father James. N. Thompson then drove to Parkland.
After they arrived, Huber said he was escorted to the emergency room where he saw the body of the president covered with a sheet. Huber said he removed the sheet from Kennedy's forehead and administered the Last Rites of the Church and, because of his condition, the Sacraments of Penance and Extreme Unction followed by the Apolistic Blessing.
"After this I recited for the President, from the ritual, prayers for the dying and for the repose of his soul, to which was added: 'Eternal rest grant unto him, O Lord, and let perpetual light shine up on him. May he rest in peace. Amen.'"
Huber said the first lady remained at her husband's side as she and others familiar with the prayers answered those with which they were familiar. He said she then kissed the president before placing her wedding ring on his finger, which Huber said he was told signified, "Together in life, together in death."
Huber said they then entered a corridor where the first lady thanked him and asked him to pray for the president -- which he assured her he would do. Huber then returned to the Holy Trinity rectory.
Shortly after 1 p.m., President John F. Kennedy was declared dead by Dr. William Kemp Clark.† According to the Warren Report, because it was impossible to determine exactly when life left the president, the time was fixed at 1 p.m. as an approximation.
††Source: Baylor.edu - Materials of Frank Jasek related to JFK and Father Oscar L. Huber -- Click on "Images - Father Oscar L. Huber, C.M. Materials" to read his entire account of the day of the assassination.