In most mass murders, there's no need for an investigation. The killer is usually dead at the scene, done in by his own hand or by a bullet from police.

The massacre of seven people last weekend at Brown's Chicken & Pasta in Palatine was not like most mass murders.

There was no killer lying dead, no clear motive, no obvious link between the victims and their assailants.So police are left with a daunting task: finding the killers, even as their trail grows colder.

The 60 members of the investigative task force have no eyewitnesses, have not recovered the murder weapons and have yet to identify any primary suspects. And the clock is ticking.

"The longer it goes, the more chance you have of developing more information," said Cmdr. James Maurer of the Chicago Police Department, looking at the bright side. "But as a general rule, the longer homicide cases go, the harder it is to reach a conclusion."

On top of the time pressures, investigators are laboring under intense public scrutiny, where their mistakes are magnified and their leads can take on unwarranted significance.

Take, for example, the arrest Friday afternoon of a Schaumburg man wanted on two warrants unrelated to the Palatine case.

After police reportedly got a tip that the man may have been involved in the massacre, they looked into his history, staked out his home and then brought him in.

If he ended up being connected to the crime, as now appears unlikely, it would be hailed as a great move; if he didn't, well, he was wanted on other charges anyway.

It was basic work. Get a lead, check it out and follow it up. But under the glare of media lights and community interest, the arrest was momentarily deemed a major break in the case.

Investigators, and the community still grieving over the seven deaths, face more days like Friday because there is no handbook for solving mass murders. It's a basic homicide investigation, only the physical evidence is greater, the spotlight is brighter and the stakes are higher.

"What it boils down to in any homicide investigation is shoe leather," said Maurer, who has been involved in thousands of homicide investigations in Chicago. "It takes a lot of walking and a lot of talking, it takes following things that lead you absolutely nowhere."

It also may take something else.

"They'll need some luck," said Jack Levin, a professor of criminology at Northeastern University in Boston and the author of "Mass Murder: America's Growing Menace."

"Mass murders have never been a challenge to law enforcement, and they still aren't, because the vast majority of mass murders are resolved at the scene," Levin said. "Most times where that's not the case, it's killers who commit armed robbery and then kill large numbers to eliminate witnesses."

Often, Levin said, those crimes are solved only when police catch a break.

"One of the killers makes a mistake and is arrested, or searched, or brought in on another charge and then snitches," Levin said.

That was the case in 1979, when Verna Stafford was arrested by police investigating the murder of six people at a Sirloin Stockade restaurant in Oklahoma City in July 1978.

Stafford told police where her husband, Roger Dale, was living, then testified against him at his trial. He ended up on Death Row; she is serving 30 years to life in prison for her role in the massacre.