SAN FRANCISCO -- On this much, mental health and law enforcement specialists who observe murder cases agree: Guilt wears many faces.
There is no list of behaviors that murder suspects have in common, they say. There is no right or wrong way to act when a loved one is killed. But a particular emotional response in the context of crime scene evidence can be an important clue, they say.
"They may do some strange things," said Christiane Tellefsen, head of the forensic psychology division at the University of Maryland. "People may go crazy, psychotic. They may not sleep well and start acting guilty."
As prosecutors prepare to present their final witness this week in Scott Peterson's murder trial, many witnesses have testified in one way or another that Peterson acted like a guilty man.
Among other things, they say he lied, again and again, not only to police but also to his friends and family.
For example, the day he attended a vigil for his missing wife, Laci, Peterson was on the phone with his girlfriend, calling her "sweetie." He hovered nearby as divers searched San Francisco Bay for the bodies, then showed up in Southern California with bleached hair, his brother's driver's license, and more than $10,000 in cash.
To many, Peterson did not act like a grieving husband.
But what does "guilty" look like? What is "normal" for a man who has lost his pregnant wife?
Many observers said Dr. Sam Sheppard acted guilty, too.
Like Peterson, Sheppard was accused, in 1954, of killing his pregnant wife. Also like Peterson, Sheppard gave conflicting accounts and lied about having an affair. He was convicted of murder and spent 10 years in prison before he was retried and acquitted.
Suspicions also were raised about Jens Sund, whose wife and daughter disappeared during a visit to Yosemite National Park in 1999.
Sund said he was only slightly concerned when they failed to meet him at an airport. He continued on to Phoenix and played golf before reporting them missing.
The cloud over Sund evaporated only after Cary Stayner confessed to their grisly slayings and was sentenced to death.
Fingers pointed at John and Patsy Ramsey in the 1996 killing of their daughter, Jon Benet, a 6-year-old beauty pageant queen.
The couple remain under "an umbrella of suspicion" in the case although no one has been arrested for the killing. Police said Patsy Ramsey flew into a rage during her interviews with police, proving that she was capable of murder.
Mike Bumcrot, a longtime homicide investigator who recently retired from the Los Angeles County Sheriff's Department, said that if a husband is not involved in his wife's murder, he will show a lot of genuine emotion. But if he is involved, "sometimes you'll see phony emotion," he said.
Bumcrot, who now works as a consultant for the department as an instructor, said he tells recruits to rely on their experience and instinct when investigating a murder.
"It's just the feeling you get after handling hundreds of murders," he said, explaining when a detective begins to suspect a person is guilty. "The hair on the back of your neck raises up."
But most mental health specialists agree there is no behavior that should be considered suspicious, in and of itself.
"Someone who values being calm is going to show less emotion," said George Bonanno, psychology professor at Columbia University. "That doesn't mean there's anything wrong with them."