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The end came viciously for a mother and her young daughter.

And it came, Las Vegas police say, at the hands of Bryan Devonte Clay Jr., who broke into their home at about 2 a.m. last week, tormented a family, sexually assaulted the mother and her daughter, 10, and then bludgeoned them to death with a hammer.

The father lay in critical condition in the blood-splattered house for more than 24 hours with his two terrified sons, ages 9 and 4, unsure what to do.

But the boys knew their dad, Arturo Martinez, an illegal Mexican immigrant who worked as an electrician by day and coached boxing to teens in the evening, always stressed how important school is, their aunt told The Associated Press on Monday.

"The first thing he always tells kids is that he will teach them, but they have to do well in school," Gaudia Martinez said.

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So the next morning, April 16, the fourth-grader walked four blocks to his elementary school and told a trusted teacher that his mom and sister were dead at home. School officials called police.

"He also reported his father had two holes in his head, was acting strange and there was blood all over the home," Las Vegas police said in a chillingly detailed arrest report made public Monday.

Neither the boys nor Arturo Martinez, 39, who remained Monday in a medically induced coma at a Las Vegas hospital, could tell investigators what happened. He is said to have severe head injuries. Rumors swirled for several days as police backtracked from initial assurances that they didn't think an intruder was involved.

Police now say the keys to solving the intense 11-day investigation were a DNA match to evidence of the sex assault on 38-year-old Ignacia Yadira Martinez, a bloody thumbprint from the house, and a baseball cap and cellphone records pointing to the 22-year-old man now facing charges that could get him the death penalty.

Clay was arrested Friday morning on a warrant in an unrelated case, then linked to the slayings after jailers obtained a warrant and a DNA sample. He was booked late Friday in the slayings and sex assaults.

Las Vegas Police Lt. Ray Steiber, who characterized the slayings as "savage" and "heinous," said investigators don't know why Clay, who had no connection to the family, allegedly picked the Martinez home. Steiber said the intruder apparently entered through an unlocked front or back door.

But "the physical evidence, including DNA, makes us confident we have the right person and he is the only person involved in these crimes," Steiber said.

Clay was being held Monday at the Clark County jail without bail pending an initial court appearance Wednesday on charges including murder, kidnapping, assault with a deadly weapon and sex assault with a minor under 14. He did not yet have an attorney.

The two boys were placed in protective custody with the Clark County Department of Family Services.

Child forensic counselors have spoken with the boys, but Nichols said police haven't questioned the children directly about what happened in the house.

"We're not going to push them," the police lieutenant said. "You can only imagine what they saw."

Clark County District Attorney Steve Wolfson said Monday that the case was getting "the highest degree of attention" from prosecutors. A decision whether to seek the death penalty won't be made for several weeks.

A public defender may be named to represent Clay, said Daren Richards, an administrator in the Clark County public defender's office.

Clay also faces a court appearance Tuesday on the original warrant accusing him of failing to appear April 3 on a felony summons in a child abuse case involving a teenage girlfriend, police and court officials said. Justice of the Peace Melissa Saragosa also has scheduled a hearing for Clay on yet another pending felony case accusing him of robbery and domestic battery.

Clay told Las Vegas police that he partied heavily with alcohol, Ecstasy and PCP, and didn't remember the home invasion, sex attacks and hammer slayings of the mother of three known as "Yady" and her 10-year-old daughter, Karla Edith Martinez, and the near-fatal bludgeoning of Arturo Martinez.

"He did not deny being involved," police said in their report, "only ... (that) he did not remember what happened."

Police added that Clay told detectives they should "kill him now instead of taking him to jail."

Authorities allege that after leaving his brother's home less than a half-mile from the Martinez home, Clay followed a 50-year-old woman on a nearby neighborhood street and tried to rape her before she clobbered him with a rock.

The woman managed to call 911 before the attacker escaped with her cellphone. Officers who found the woman about 2 a.m. April 15 also found a baseball cap that Clay later acknowledged was his, according to the police report.

Investigators think the home invasion attacks occurred between about 2 a.m. April 15, when several calls were placed with the phone taken from the 50-year-old woman, and just after 4 a.m., when there was a final call, Steiber said.

The calls were to acquaintances of Clay, including a 17-year-old girl and two people who Clay later told detectives would be "the first people he would call if he was in trouble or scared." Clay denied making the calls.

The crucial break came when a DNA sample collected from Clay following his arrest on the child abuse charge matched evidence from the attempted rape and the attacks at the Martinez home, Steiber said.

Clay's DNA was also was found on blood spots on the woman's jacket, Steiber said. Tests are still being conducted on a T-shirt and jacket that a neighbor found wadded up on the rear tire of his pickup truck. The neighbor told police he thought the clothes belonged to Martinez so he tossed them into the bed of Arturo Martinez' pickup.

Police have a claw hammer believed to be the murder weapon, Steiber said. He wouldn't say where it was found.

Steiber said Clay had only traffic offenses before his arrest Friday morning at his mother's home in northeast Las Vegas on a warrant charging him with felony child abuse in a separate case involving a teenage girlfriend. He had not been formally charged.

Gaudia Martinez said she has visited her brother in the hospital, but he hasn't been able to communicate.

"The boys are OK. Thank God, physically OK," their aunt said.

This story is based on a reporting by The Associated Press.

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