A prosecutor urged jurors Friday to "follow the trail of blood" from the bodies of three butchered children to two of their family members to find those two men guilty of murder.

Assistant State's Attorney Sharon R. Holback said that blood and DNA evidence would link Policarpio Espinoza Perez, 23, and his nephew, Adan Espinoza Canela, 18, to the slayings of the children, members of an extended family of Mexican immigrants, in May of last year.

As both sides presented opening statements, Holback offered no motive for a crime so brutal -- the children, ages 8, 9, and 10, were nearly beheaded -- that it stunned a city hardened by one of the highest homicide rates in the country. She said only that the defendants had conspired with others who she did not name and who have not been indicted.

An attorney for Espinoza Canela offered the jury two possible motives, both of which pointed to the father of his own client as the person responsible for the killings of the children.

James Rhodes told jurors that Victor Espinoza Perez, who is also the brother of the other defendant, may have orchestrated the slayings because he had fallen out with his wife after making romantic advances toward the mother of one of the children. He did not explain precisely why he would have then slain the woman's child and her aunt's two children.

In an alternative scenario, Rhodes said, Victor Espinoza Perez may have been involved in smuggling illegal immigrants from Mexico into the United States, a service for which he might have charged $2,500 a person. Under that theory, a person Rhodes did not name owed money for the service and Espinoza Perez "decided he was going to send a message."

An attorney for Policarpio Espinoza Perez, meanwhile, told jurors that both defendants were wrongly accused by police who, under intense public pressure to solve a crime, "had to arrest someone." His "unlearned and unsophisticated" client was merely a convenient target, lawyer Timothy Dixon said.

"It's easy to do, and you're going to see how the police did it," he told the jury.

The victims were Ricardo Espinoza, 9, his sister Lucero Espinoza, 8, and Alexis Espejo Quezada, 10, a relative of theirs. The first day of the trial added new detail to the public account of their gruesome slayings, in a cramped apartment the children shared with four other family members, and presented a series of unusual courtroom twists.

First, Rhodes distanced his client from the other defendant in dramatic fashion. After offering his two theories of motive, Rhodes told jurors that phone records would show that Policarpio Espinoza Perez was in close contact with Victor Espinoza Perez and the second man's wife on the day of the killings. The phone calls started early that morning and then stopped at the time of the slayings, only to resume afterward, Rhodes said.

And the father of two of the victims, Ricardo Espinoza Perez, told jurors that he does not believe Espinoza Canela is guilty. Other family members have said as much publicly, but it was nonetheless unusual to hear a prosecution witness declare a defendant's innocence. Ricardo Espinoza Perez was not asked if he believed the other defendant to be guilty.

Holback called Ricardo Espinoza Perez to the stand and questioned him aggressively, pressing him to explain why neither he nor his wife had keys to their apartment on the days of the slaying, why he climbed in through a high kitchen window when a more accessible window was open, and why he kept a large knife -- she did not say whether it was the weapon -- under his sink.

She did not ask him to describe the scene he came upon once inside the apartment or to discuss his reactions to the killings of his two children, the type of testimony prosecutors in such cases typically elicit.

Finally, there was the testimony of Victor Espinoza Perez. Through an interpreter, he said he did not know his son Adan Espinoza Canela's age or birthdate. Holback then asked him how many children he had.

"I think that's not a question that needs to be answered here, right?" he replied.

She pressed. He relented and said seven. Then he said nine -- none of whose ages or dates of birth he knew.

In her opening statements, Holback had said each victim was beaten over the head with a baseball bat. The boys were also strangled, she said, one with a telephone cord, the other with bare hands.

Still, she said, all three were alive, and they struggled until their heads were cut nearly off with what Holback described as a sawing motion.

"This was not quick," Holback said. "This slaughter was brutal and slow."

Although it had been widely reported that one of the children was decapitated, Holback said their heads remained attached. In one case, she said, by "less than an inch of skin."