Yolanda Saldivar came into Selena Quintanilla Perez's life in 1991, a nurse eager to organize the first fan club for the rising Mexican American singing star.

By early this year, however, Selena's family had begun to suspect Saldivar of darker motives and concluded she had siphoned money from the entertainer's accounts. But today, in opening statements during Saldivar's murder trial in the slaying of the singer, defense attorneys suggested there was a different villain in the story of the pop singer's death: Selena's father and manager, Abraham Quintanilla Jr.

"The evidence will show that Abraham Quintanilla started efforts to split up this relationship," said defense attorney Douglas Tinker, as the trial opened under extremely tight security in a courtroom here. "He accused Yolanda Saldivar of being a lesbian, which is not true. Yolanda was a challenge to the control Abraham Quintanilla had over Selena."

The Grammy award-winning singer, who was a few weeks shy of her 24th birthday, was shot once in the back around noon March 31 at a Days Inn motel in her home town of Corpus Christi. She reportedly had agreed to meet Saldivar there to retrieve some financial records. Quintanilla has said he had fired Saldivar, who also worked as manager of Selena's fashion boutiques in San Antonio and Corpus Christi, shortly before the shooting, but Tinker told the jury that Selena and Saldivar were arguing that day over Saldivar's decision to quit her job.

Saldivar had recently purchased a gun, Tinker said, because she was fearful of Abraham Quintanilla and, distraught over the turn events had taken, was threatening to kill herself in the motel room. As Selena began to move away from her, Saldivar waved the gun and it accidentally discharged, he said. During the next nine hours, he said, as Saldivar sat in her truck in the motel parking lot with the gun to her head, she repeatedly told police over a cellular telephone, "I didn't mean to shoot her."

In his opening statement, however, prosecutor Carlos Valdez told the jury of six men and six women that Selena "was killed in a senseless and cowardly act of violence."

"She shot her in the back, severing an artery, causing Selena Quintanilla Perez to bleed to death," he said. "Nothing says we have to prove why this happened. It is difficult to get into someone's head. But you will be able to glean from the evidence why."

The sudden death of the singer, just as she was about to realize wider success as a pop entertainer, has reverberated deeply within the nation's Hispanic communities. Known for her lively dancing, her revealing outfits and her infectious songs -- "Bidi Bidi Bom Bom" was an early hit -- Selena was considered a wholesome role model by thousands of young teenagers and their parents. After her death, her first English-language album, "Dreaming of You," debuted at No. 1 on the Billboard charts, and outside the courtroom this week, fans in Selena T-shirts were still shedding tears at her memory.

As the prosecution's first witness today, Abraham Quintanilla provided a portrait of a musical family that rose from modest beginnings, singing at the family restaurant in Lake Jackson, Tex., to drawing crowds of 80,000 at regional concerts. With the youngest child, Selena, as the vocalist, the band Los Dinos "traveled all over the state of Texas in an old Ford van, with a homemade trailer," he said. "The whole family went, including the dog. I saw a talent and I encouraged it."

Quintanilla, who was not cross-examined today by Tinker, told Valdez that he had never tried to control his children, beyond guiding them to do "the correct thing," and that he did not try, as Tinker charged, "to live vicariously" through his daughter. He admitted that, because of traveling, he had allowed Selena to drop out of school after only a few months in the eighth grade, but said she continued her education through correspondence courses. By the late 1980s, the hard work had begun to pay off, and Selena dominated the regional Tejano Music Awards, winning Entertainer of the Year for her rendition of the updated Tex-Mex style.

Quintanilla denied that he had ever accused Saldivar of being a lesbian. He said he began investigating her accounting earlier this year when he got numerous complaints from fans who said they had not received mementos they had paid for.

"Selena's image was being tarnished," he said. "People were blaming her."

It didn't take long, he said, to accumulate enough evidence to demand a final meeting with Saldivar, which led to the fatal session with his daughter.