(CNN) -- Delaware authorities are investigating the circumstances surrounding the recent discovery of the body of a former Pentagon official in a landfill, according to a statement released Monday by the Newark, Delaware, Police Department.

The Delaware medical examiner's office has ruled the death of 66-year-old John P. Wheeler a homicide.

Wheeler was discovered at Wilmington's Cherry Island Landfill on December 31.

Wheeler, who lived in New Castle, worked under three Republican presidents -- Ronald Reagan, George H.W. Bush, and George W. Bush. He served as a special assistant to the Air Force secretary from 2005 to 2008.

Among other things, he also served as head of the Vietnam Veterans Memorial Fund and was the first chairman of Mothers Against Drunk Driving.

A staff officer in Vietnam, Wheeler was a graduate of West Point, as well as Harvard Business School and Yale Law School.

"We are asking for the public's assistance" in the case, Newark police spokesman Lt. Mark Farrall told CNN. "We don't know where the crime scene occurred. The body was dumped within our jurisdiction." Newark is about 12 miles southwest of Wilmington.

Farrall noted that Wheeler's body was seen jutting out of a garbage truck at the landfill by a spotter whose job it is to ensure that hazardous material is not dumped there.

Police believe Wheeler's body was most likely picked up by the truck at one of the first of ten specially designated dumpster pick-up spots before heading to the landfill.

Farrall said police do not know when Wheeler was last seen. He noted that Wheeler had been scheduled to take a train from Washington to Wilmington near the time of the death, though he dismissed reports that Wheeler had actually been seen on a train.

Farrall said an apparent dispute between Wheeler and a neighbor was "one facet of the investigation."

Wheeler's attorney, Bayard Marin, told CNN that his client had been involved in a lengthy legal fight with a couple building a new home across the street in a historic district of New Castle. Wheeler had adamantly opposed the new construction.

The dispute may have become contentious, but "I can't recall a confrontation," Marin said. "Everything seemed to be kept within normal bounds."

The Newark Police Department released a statement on behalf of Wheeler's family.

"As you must appreciate, this is a tragic time for the family. We are grieving our loss. Please understand that the family has no further comment at this time. We trust that everyone will respect the family's privacy," the family said.

Veterans advocates offered statements of praise for the former official, who served in Vietnam.

"It is only fitting that we pause now and remember Jack Wheeler, who served his country honorably, then dedicated himself to ensuring that our nation's service members are always given the respect they deserve," said Jan Scruggs, president of the Vietnam Veterans Memorial Fund.

What Wheeler "cared about was civic values and civic virtue," wrote James Fallows, national correspondent for The Atlantic.

"He was a complicated man of very intense (and sometimes changeable) friendships, passions, and causes. ... I feel terrible for his family and hope they will eventually find comfort in knowing how many important things he achieved."

CNN's Alan Silverleib, Allan Chernoff, Sarah Baker, and Nina Golgowski contributed to this story