Updated: With response from ABC News with victims families’ request for interview.

Kelly Wang and Jinshuang "Jane" Liu, the mothers of two murdered Santa Barbra students, look at burial plots for their sons at a cemetery in California. (Peter DaSilva/for The Washington Post)

Inside a two-bedroom beachside apartment, Elliot Rodger began his Santa Barbara rampage last month by mutilating his two roommates and their friend. The scene, police said, was horrific.

But there were few signs of a struggle, according to the victims’ parents. There was no blood on the walls or ceiling, and the confrontation between Rodger and the three other young men seemed to have been confined to a small space, the parents said on the basis of a visit to the crime scene. They said evidence taken from the apartment makes them think that Rodger may have used a machete, knives and a hammer to kill their sons.

“How did one boy do this? Our sons, there were three of them. . . . We wonder, were our boys drugged?” Junan Chen, the father of George Chen, 19, said in an interview.

After Rodger killed them May 23, he set out in his black BMW and later on foot, fatally shooting three strangers and then committing suicide. Those latter killings happened in public view — in a store and in front of a sorority house — but the first three occurred behind closed doors in the shared apartment, and the Santa Barbara County Sheriff’s Office has disclosed few details about what happened there.

The parents of the three college students who were stabbed said it took them weeks to muster the courage to speak publicly about the killings. They said they finally did so in a joint interview to air their frustration with authorities’ handling of the case and the scant information that has been provided.

The three families — all Chinese immigrants who said they came to the United States for a better life — said that they are disturbed by a culture that seems more interested in the killer than in their sons. They also are angered by public-health and legal systems that they say value the rights of the mentally ill, including Rodger’s, over those who may become their victims.

“It may be too late for our kids, but I don’t want it to be too late for other American children,” said Henry Hong, the father of Cheng Yuan “James” Hong. “The system is clearly broken. It should have protected our sons, who were so innocent and trusting.”

In the aftermath of the rampage, public debate has again focused on gun violence, largely ignoring the devastating harm done by the triple stabbing.

James Hong and Weihan “David” Wang, both 20, were Rodger’s roommates, and Chen was their friend. They were students at the University of California at Santa Barbara’s College of Engineering, where they met during their freshman year.

The boys’ fathers visited the crime scene a week after the killings with the help of the apartment manager, and Junan Chen described what they saw. They also shared information with their attorney, Todd Becker, who provided details in an interview.

Police had removed a 6-by-5-foot piece of carpeting in the bedroom the roommates shared. A swath of vinyl flooring around the toilet had been cut away. A few feet of carpeting between the bedroom and bathroom had been cleaned. The limited amount of material removed from the apartment suggested that any altercation occurred in a confined space, the parents said.

The families said the sheriff’s department has declined to tell them what the evidence revealed.

“The Sheriff’s Office owes it to the victim’s families and to the public to not prematurely release information before we have all of the facts in this case,” Kelly Hoover, a department spokeswoman, said in a written statement. A report on the police investigation and the coroner’s findings are expected in a few weeks.

But beyond the lack of information, the parents are especially angry with the department over what they say were several missed opportunities to recognize how troubled Rodger was and thus prevent the killings.

The first chance that was missed, they alleged, came in July 2013, when Rodger pretended to shoot people with an imaginary gun at a party in Isla Vista and then tried to push several women at the party off a 10-foot-high ledge. When sheriff’s deputies interviewed him the following day at Goleta Valley Cottage Hospital, where he was being treated for a broken ankle, they concluded that he had instigated the incident, a sheriff’s department report shows. Deputies did not arrest him or investigate further.

“They didn’t do anything,” said Kelly Wang, George Chen’s mother. “Why?”

The parents said another opportunity came six months later, when Rodger called 911 to report that Hong had stolen candles from him that were worth $22. Rodger insisted that the deputies take action. Hong was handcuffed, arrested and taken to jail, a police report shows.

“At this point, police should have known there was something wrong with this boy,” Henry Hong said. “He called 911 over candles. . . . It was a minor thing between roommates.”

It is the third encounter between deputies and Rodger that most upsets the parents. One month before the killings, Rodger’s mother had alerted the sheriff’s office to his deteriorating mental state, telling the department about disturbing videos her son had posted on YouTube.

In response, deputies went to Rodger’s apartment but did not view the videos. Nor did they check a state database that would have revealed that he had recently bought three semiautomatic pistols.

In a manifesto he prepared, Rodger wrote: “If they had demanded to search my room . . . [t]hat would have ended everything. For a few horrible seconds, I thought it was all over.”

Instead, the deputies left his apartment after finding Rodger to be “shy, timid, polite and well-spoken,” in the words of Santa Barbara County Sheriff Bill Brown.

“If they went in, they would have also found the knives,” Kelly Wang said. “Our boys would still be with us.”

Brown has defended his department in previous interviews, saying Rodger was able to hide his violent tendencies and “fly under the radar.”

The three families are lobbying the news media to shift their attention to the victims. After ABC News announced June 9 that Barbara Walters would be coming out of retirement to interview the killer’s father, the families banded together and e-mailed a producer June 13.

“As parents, we plea you [the media] not to focus on the killer side,” the families said in the e-mail, which was provided to The Washington Post. They asked that the network instead “pay respect to the six beautiful live[s] that [were] gone too soon.”

In response, ABC News spoke with Becker, the families’ attorney late Friday afternoon, and the network is now in discussions with him about interviewing some or all of his clients.

Alice Crites and Julie Tate contributed to this report.