LAS CRUCES, N.M. - The killers were ruthless.

They showed up at the Las Cruces Bowl shortly before it was scheduled to open at 8 a.m. on a quiet Saturday, just an ordinary sleepy weekend in a laid-back college town about 40 miles north of the Mexican border.

After stepping through an unlocked door, the two men herded a snack bar cook, Ida Holguin, bowling alley manager Stephanie Senac, her 12-year-old daughter, Melissia Repass, and the girl's 13-year-old friend, Amy Hauser, into a corner office.

Making no effort to conceal their identities, they brandished a small-caliber pistol and grabbed as much as $5,000 from a safe.

Bowling alley mechanic Steve Teran reported for work and walked in on the crime, along with his 6-year-old daughter, Paula Holguin, and 2-year-old daughter, Valerie Teran, because he didn't have a babysitter that day. Repass and Hauser were there that morning to supervise the nursery.

The assailants lined up all seven victims on the floor in the cramped office, shooting each in the head multiple times at close range. Killed in the rampage were Hauser, Teran and both of his young girls.

The killers set fire to the office and fled.

It happened Feb. 10, 1990, a day that will always be remembered for what quickly became known as the Las Cruces bowling alley massacre, the worst mass murder in the history of this southern New Mexico city.

Despite intense efforts by authorities, the murderers' identities remain a mystery 21 years later.

"Some people just do all the right things before, during and after a crime to elude capture," said police detective Mark Myers, who has worked the case since 2002. "Anytime you have a high-profile crime like this, believe me, everything you can imagine has been thrown at this case."

Repass and Senac survived the shooting, although Senac died a few years ago.

Survivor Ida Holguin, the cook, who is unrelated to Paula Holguin, told police the gunmen seemed startled by the number of people they encountered.

Police say they took $4,000 to $5,000 but, strangely, left behind an undisclosed amount of cash.

Frustrated investigators are still chasing leads, still working to keep the case in the headlines in a desperate hope that someone will come forward with a tip that breaks it open. It's an agonizingly long time for the victims' families to have no resolution.

"You wait and wait and wait," Audrey Teran, who lost her husband and daughters, told The Associated Press last week. "The first few years, maybe the first 12 years, there was always a lot of anxiety. I was always very antsy and wanting to know more. But after that, I had to put it aside and deal with my anxiety. We've gotten to a point where we just don't get any answers."

Despite being critically injured, Repass, the 12-year-old, managed to call 911 from the burning office.

"They told us all to get down. They shot me five times," she is heard saying on a scratchy audio replay of the call.

A dispatcher assured her that help was coming and asked how many people were shot.

"One, two, three, four, five, six, seven," she counted.

Repass told the dispatcher about the fire and said, "Please hurry. There's a bullet in my head."

From the beginning, the case presented major problems for investigators.

For starters, police officers were confronted by flames that were consuming the office and destroying evidence.

Firefighters wiped out more clues when they opened their hoses. And of course, the first-responders had to tend to the gunshot victims.

By the time those issues were addressed and the victims en route for medical treatment, Myers said responding officers finally comprehended the enormity of the site - a bowling alley - and realized the building hadn't been secured during the rush to save survivors and douse the fire.

"It was a very complicated crime scene," Myers said, adding that what police have confirmed only substantiates his belief that the act was premeditated.

"They lit the office on fire," he said. "That's a clear indication they were thinking about destroying evidence they had left behind. They weren't going to leave any witnesses, no matter how young. I have no doubt when they left, they thought everyone in there was dead."

Another major issue: Forensics of the time focused on gathering fingerprints, a primitive measure compared with high-tech crime solving approaches seen today.

"We did recover fingerprints but it was a bowling alley. You would expect to find that," Myers said. The getaway was as puzzling as the crime. As investigators cased the bowling alley, looking for clues, police and other law enforcement agencies blocked roads out of town, carefully screening anyone driving past.

But Myers acknowledged that it could have easily beat the roadblocks if they had driven straight away.

The survivors gave descriptions of the killers to police. Both were Hispanic, one about 30, with dark wavy hair, light-colored eyes and no accent in his speech. The other was about 45 to 50 with thinning salt-and-pepper hair, a dark complexion and a slight Spanish accent.

Myers said he thinks someone has information that could help, saying that person hasn't had the courage to come forward or perhaps believes a nagging suspicion couldn't be true.

Teran, now 45, said she feels sadness when she sees friends posting Facebook photographs of their grandchildren, thinking she might be a grandmother today if her young daughters had not been shot.

She said she feels strongly that the killers are still out there.

"I picture them hurting and hiding," she said. "It can't be too easy. Everyone is looking for you while you're trying to make a normal life for yourself. I picture them in a lot of misery."