Police say DNA on leftover pizza crust helped lead them to a murder suspect in Northwest Washington. An expert from the National Museum of Crime & Punishment explains how DNA investigations work and how even the littlest piece of evidence can help. (Alice Li/The Washington Post)

D.C. police are searching for a suspect they believe is connected to the deaths of four people at a home in an upscale Washington neighborhood. The critical clue that led police to 34-year old Daron Dylon Wint: A leftover pizza crust.

Three law enforcement officials with knowledge of the investigation told The Washington Post on Wednesday that Wint was a match for DNA evidence left on the crust of a Domino’s pizza delivered to the home on May 13.

They believe that Savvas Savopoulos, 46; Amy Savopoulos, 47; their 10-year-old son, Philip; and housekeeper Veralicia Figueroa, 57, were held captive overnight in the multimillion-dollar Northwest Washington home, then killed before the house was set afire the following day.

[Suspect in quadruple killings worked for victims’ family business, police say]

Despite the fact that the home had been burned, D.C. Police Chief Cathy L. Lanier said Tuesday that investigators had been able to collect quite a lot of evidence from the scene, including a video and DNA samples.

Hunger and perhaps an oversight may have caused the suspect to leave a critical clue in this growing murder mystery that has captivated and terrified Washington.

“It’s not unusual for criminals to leave their evidence behind,” Lawrence Kobilinsky, an expert on DNA technology, told The Post on Thursday. “In fact, it’s quite common.”

D.C. police have an arrest warrant for a 34-year-old man, Daron Dylon Wint from Maryland. Law enforcement sources said DNA evidence linked him to the killing of Savvas Savopoulos, his wife, young son and housekeeper. (Jhaan Elker/The Washington Post)

During home break-ins, criminals are often known to do something very simple: Eat.

“They usually do strange things,” noted Kobilinsky, chair of the forensic sciences department at the City University of New York. “They’ll eat food from the refrigerator and thereby leave their DNA. Or they’ll leave their cigarette butts and leave their saliva. They just seem to go out of their way to leave their calling card behind.”

[Woman being held hostage uses Pizza Hut order to raise alarm and summon the police]

Savvas Savopoulos and Amy Savopoulos at the Starlight Children’s Foundation MidAtlantic’s Wine Dinner in 2008. (Tony Powell/Washington Life Magazine) Veralicia Figueroa (Family photo)

Four years ago, police arrested a man they suspected to be the elusive East Coast rapist after collecting one of his discarded cigarette butts and making a DNA match. That man, Aaron Thomas, was eventually sentenced to life in prison.

From a forensic standpoint, finding a partially eaten piece of pizza — or a spent cigarette butt — is like stumbling upon a pot of gold. And in the case of the quadruple homicide, the task of determining when the DNA had been left was made infinitely easier because police were able to quickly learn that a Domino’s driver had delivered the pizza to the home around the time the crime was being committed.

A law enforcement source noted that the suspect appeared to have eaten the pizza with gloves on, not realizing that his saliva was being left behind.​

“In the case of crust, you probably have bite marks,” Kobilinsky said. “You’re talking about saliva, and saliva has a lot of DNA.”

[Slain housekeeper planned to join kids in El Salvador]

So much DNA, in fact, that once investigators extracted a sample, they might have had to dilute it in order to conduct a test, whereas shed cell samples that might be left behind on anything a suspect touched would be more difficult to extract in large enough quantities to test.

Tests on the pizza crust were conducted by the Bureau of Alcohol, Tobacco, Firearms and Explosives, according to a law enforcement source. (Last month, the District’s own crime lab was ordered to suspend all DNA casework after a national organization that governs DNA laboratories concluded that the new lab’s procedures were “insufficient and inadequate.”)

The DNA profile from the crust could be matched to convicts or suspects in other crimes from either local, state or federal databases.

“The reason why this works for law enforcement is that most of these guys are recidivists,” Kobilinsky said. “If they were not in the database, [investigators] wouldn’t be able to identify them.”

With a potential match in the database, investigators would then need to test an actual DNA sample taken from the suspect — a cheek swab, usually — and compare it to the sample taken from the crime scene. At that point, investigators would be more certain that they were looking for the right person.

Human error is, of course, possible. But in general, Kobilinsky says, DNA evidence — especially from a high-quality saliva sample that one might get from a bitten pizza crust — is pretty accurate.

“It’s almost redundant to say that DNA remains the gold standard of forensics,” Kobilinsky said. “And compared to any other type of analysis, DNA is at the highest level. It’s in an exalted status.”