Defense in Murder Case Challenges Use of Tape as Evidence : Trial: The judge must decide if suspect Mark Thornton’s jailhouse talk with his grandmother can be used against him. He is accused of killing a Westlake nurse.

Ventura County sheriff’s investigators illegally taped a jailhouse conversation between Thousand Oaks murder suspect Mark Scott Thornton and his grandmother, defense attorneys said Wednesday, asking a judge to prohibit prosecutors from using it at trial.

Prosecutors are seeking the death penalty against 19-year-old Thornton, who they say kidnaped and fatally shot Westlake nurse Kellie O’Sullivan during a carjacking last September.

Ventura County Superior Court Judge Charles R. McGrath began a hearing Wednesday to determine whether he will allow the tape to be presented as evidence in the Thornton trial, which is set to start with jury selection Sept. 19.

The outcome of the evidentiary hearing, which is expected to continue this morning and wrap up on Monday, will be crucial to the trial, lawyers on both sides contend.

Neither side would reveal Wednesday what specific information is contained on the audio tape, which was marked as an exhibit in court but not played on Wednesday. A 33-page transcript of the tape also was provided to the judge, who ordered the document sealed from the media and the public.

Six days after O’Sullivan disappeared Sept. 14, 1993, Thornton was arrested in Reno, Nev. on suspicion of kidnaping his girlfriend and shooting at the girl’s mother. He was carrying a handgun when arrested and had the keys to O’Sullivan’s 1991 Ford Explorer in his pocket. The truck was found nearby.

On Sept. 26, the same day Thornton was extradited to Ventura County, O’Sullivan’s body was found amid brush in the Santa Monica Mountains in Los Angeles County. She had been shot twice in the back and once in the chest, according to court testimony. Eight days later, on Oct. 4, Thornton was charged with O’Sullivan’s murder.

The day Thornton was extradited, Ventura County Sheriff’s Detective Susan Creed drove 110 miles to Oceano and visited Thornton’s grandmother, Lois Thornton, Creed testified Wednesday.

Creed offered Lois Thornton a ride back to Ventura County so she could talk with her grandson, Creed said. Creed testified that the defendant and his grandmother have a close relationship.

Creed’s supervisor, Sgt. Mike Barnes, testified that he told the grandmother before she talked to her grandson that the defendant was suspected of kidnaping his girlfriend, 16-year-old Stephanie Campbell, shooting at Campbell’s mother and killing O’Sullivan.

Barnes testified that the grandmother was aware her conversation with the defendant was being taped, although he said that Mark Thornton was not aware of that fact.

Defense attorneys, in court papers, say the tape of the 55-minute conversation should not be allowed in evidence at Thornton’s trial, because he was entitled to privacy.

Neither Creed nor Barnes alluded to the content of the tape during their testimony before McGrath on Wednesday.

Barnes said Lois Thornton told him that her grandson had been having a strained relationship with his mother prior to his arrest. He testified that Mark Thornton had been living in a car with no money and no food.

Mark Thornton’s father was an alcoholic who abused his son, the grandmother told detectives. Thornton’s father died before his son’s arrest, Barnes testified.

Barnes said the Thornton case is not the first time he has taped a defendant’s conversations with a relative without the defendant’s knowledge. He said the method of secret taping has been upheld on appeal in previous cases.