Wheeler was found dead in a landfill on Friday, and the police have trying to retrace his movements between Dec. 28 and then.
On Tuesday, police said a witness had come forward to say that Wheeler had been spotted alive in downtown Wilmington on Thursday afternoon. That is less than 24 hours before his body was found in a Wilmington landfill in refuse that came from trash bins in one of 10 possible locations in Newark, Del.
The case has drawn national attention - Newark police received roughly 70 media calls Tuesday - because Wheeler, 66, lived such a distinguished public life.
A Vietnam veteran who became a driving force behind the controversial memorial on the National Mall, Wheeler worked on nuclear, chemical, and cyber issues at the Pentagon. He was the first chief executive officer of Mothers Against Drunk Driving, a secretary of the Securities and Exchange Commission, and a tireless advocate for veterans.
Wheeler left his office outside Washington on Dec. 28. His body was found in Wilmington on Friday. He was scheduled to take a Amtrak train from Washington to Wilmington on Thursday.
Detectives were able to verify that Wheeler had been seen Thursday near 10th and Orange Streets - close to the Hotel du Pont - but a police spokesman declined to say how this was confirmed. An executive at the nearby DuPont Corp. headquarters, which employs outdoor surveillance cameras, said that the company had "cooperated" with the police but declined to elaborate.
Police say they have no suspects and have released few details about the slaying - in part because they themselves have so many unanswered questions, including where the killing took place.
"We're still trying to [find] the crime scene," said Newark police spokesman Mark A. Farrall. "We're working a lot of leads."
Farrall has said that Wheeler died shortly before his body was discovered Friday, but has not described how Wheeler died - whether, for example, his death was caused by gunshot, bludgeoning, or some other violent act.
An official cause of death will not be released until "toxicology reports and other forensic studies" are completed, said Carl Kanefsky, a spokesman for the medical examiner.
"It's quite a mystery, and the length of time it's taking to solve it makes it more intriguing," said Bayard Marin, a lawyer who represented Wheeler in a dispute over a neighbor's plans to build a large house in New Castle's historic district.
The Wheelers tried to halt those plans in court, contending the house was too big for the neighborhood.
The incendiary devices were placed at the neighbor's home last week, police said, days before Wheeler returned from his part-time consulting job for the defense contractor Mitre Corp., located in McLean, Va., outside Washington.
Marin said he did not know if the devices or Wheeler's death had any connection to the building dispute, but he said tempers in the court case never rose to acrimonious levels.
Marin said he was interviewed by police Tuesday for 45 minutes, but he would not say what detectives asked. "I guess they are just gathering all the miscellaneous facts and hoping to tie them together to find something they can make of it," he said.
Meanwhile, in Manhattan, police on Tuesday searched the condominium that Wheeler and his wife had shared in a brick building on 124th Street for at least three years, the Associated Press reported.
Wheeler's widow, Katherine Klyce, who operates an international textile company with ties to New York and Cambodia, is unavailable for comment, according to a family statement.
The FBI on Tuesday offered "technical assistance" to the police, said FBI spokesman Rich Wolf. He declined to elaborate, but in FBI parlance, the term "technical assistance" typically refers to forensic assistance. It does not mean the FBI is conducting a full investigation.
In Delaware, authorities returned to the Cherry Island Landfill on Tuesday but kept reporters at bay.
Farrall, the police spokesman, said only, "We're looking for anything that might be of evidentiary value."
Sanitation crews used an alternative site at Cherry Island on Tuesday, so that police could comb the area where the body was found without interruption, said F. Michael Parkowski, a spokesman for the Delaware Solid Waste Authority.
Parkowski said it was not surprising that workers had discovered Wheeler's body in time to retrieve it from the landfill. He said truck drivers as well as workers known as "spotters" are trained to watch garbage for suspicious items as it is dumped at the site.
The defense contractor that had employed Wheeler part time since 2009 issued a short statement Tuesday. "At this time our thoughts are with his family," Mitre said.
The statement said Wheeler's work for Mitre consisted of "providing part-time support to outreach activities aimed at promoting discussions among government, industry, and academia on cyber defense topics." Company spokeswoman Jennifer J. Sherman declined to further explain his duties.
The cause of Wheeler's death - if it has been determined - is likely driving the focus of the investigation, said Michael Carbonell, a former FBI agent who supervised the agency's violent-crime squad in Philadelphia.
"If he died by blunt-force trauma or was shot, it tells us it was probably a random street crime, but if he's strangled, that's different," said Carbonell, who emphasized that he was merely speculating on the basis of his decades with the FBI.
The biggest publicly known clue, Carbonell said, is that the killer or killers apparently tried to hide Wheeler's corpse by placing it in a trash bin.
"Guys who rob and shoot a guy do that and run," Carbonell said. "Somebody went to some extra effort to dispose of the body."
Contact staff writer John Shiffman at 301-320-6655 or firstname.lastname@example.org.