A Dallas County jury this morning will continue deliberating the fate of a man accused of causing the death of his girlfriend's brother by giving the boy cheese heroin.

Deleon Vanegas, 20, was originally charged with murder in the death of 15-year-old Fernando Cortez Jr. But the charge was changed last month to delivery of a controlled substance to a minor, a second-degree felony. If convicted, Mr. Vanegas could be sentenced to life in prison if jurors rule that the heroin killed Fernando, and if they determine the drug acted as a deadly weapon.

Mr. Vanegas' one-day trial began Tuesday morning with his attorney, Heath Hyde, calling the teenager's death an accidental overdose. Mr. Hyde said his client and Fernando were both drug users and shared what they had on March 30, 2007.

Testimony showed that Fernando gave Mr. Vanegas some Xanax, an antidepressant, that day. And later that same day Mr. Vanegas, who was 19 at the time, gave cheese heroin to his 16-year-old girlfriend, Bianca Cortez, and Fernando. Fernando went to sleep that night and never woke up. His body was found the next day.

"The victim was just as experienced and sophisticated a drug user as Mr. Vanegas," Mr. Hyde said.

But the boy's father, Fernando Cortez Sr., and Bianca disagreed. They testified that night was the only time Fernando had used cheese heroin, a powdered mixture of black tar heroin and cold medicine so named because it resembles grated Parmesan cheese.

Prosecutor David Alex countered that even if Fernando were a regular drug user, Mr. Vanegas still broke the law when he, an adult, provided heroin to a juvenile. He said controlled substance laws were not made just for drug dealers; they also address young men and women giving drugs to children.

"If you have a dope problem, keep it to yourself," Mr. Alex said during closing arguments. "If you share with adults, it's likely nothing will happen. But when you start sharing it with our kids, we're going to hold you accountable."

In court, Mr. Alex played a videotape of Mr. Vanegas being questioned by Dallas police Detective Paul Ellzey. On it, he admitted buying the heroin and mixing it with cold medicine to make the cheese concoction. He said he gave it to Fernando.

Mr. Vanegas and Bianca had been living together in his house for a month, Bianca testified. She had planned to take Fernando to her mother's house for the weekend, but her mother was having a girls' get-together. She testified that she knew her father would not want Fernando at Mr. Vanegas' house, but she took him there anyway.

They rented movies, got Chinese takeout and stopped by a drug house to buy Xanax, Bianca testified. Mr. Vanegas had bought the cheese heroin earlier. At the house all three snorted the heroin, but only Fernando died.

Detective Ellzey testified that cheese heroin, especially when cut or diluted by inexperienced users, is like playing with a loaded gun. In the videotape of his police interview, Mr. Vanegas tells the detective he cut the cheese heroin the way he was taught.

"He's a stupid person. He didn't know what he was doing," Detective Ellzey said. "That's the reason we have kids dying from cheese."