MARTINEZ, California (CNN) -- Investigators have arrested a 16-year-old boy in connection with the killing of Pamela Vitale, wife of high-profile attorney and television legal analyst Daniel Horowitz, a sheriff's spokesman said Thursday.The suspect is from Lafayette, California, where the couple were building their dream house in the hills east of Oakland. The teenager was arrested Wednesday night and was being held in the Contra Costa County juvenile detention facility, said Jimmy Lee, a spokesman for the Contra Costa County Sheriff's Department. (Watch a report on the arrest -- 4:35)"We are still trying to establish the exact motive," Lee said. Investigators would not name the youth, Lee said. Vitale was beaten with a piece of crown molding, and a cross was carved into her back, a law enforcement official with detailed knowledge of the case said. Investigators suspect the youth was confronted while trespassing on the couple's property and probably did not go there with the intention of killing her, the official said. The teenager was arrested at a relative's home in the town of Walnut Creek, just east of Lafayette, the law enforcement official said. Horowitz said he found Vitale, 52, when he returned from San Francisco to the mobile home where the couple lived for the past two years while building a 7,000-square-foot Italian-style mansion.It was Vitale's dream house and she supervised the project down to the last detail, Horowitz told CNN.Medical examiners have concluded that Vitale died from blunt trauma to the head, said a spokesman for the Contra Costa County Sheriff's Department. "I took it all in, and I knew she was dead," Horowitz told CNN's Nancy Grace in an exclusive interview. (Watch Horowitz describe his last minutes with his wife's body -- 4:50)Horowitz told CNN he had been in San Francisco preparing for the trial of Susan Polk, accused of stabbing her millionaire husband to death in 2002. The judge declared a mistrial in the high-profile case because of Vitale's slaying.Horowitz has represented high-profile defendants and appears frequently as a legal analyst on cable television networks, including CNN.