A George Washington University graduate student who died of a head injury after an altercation in a McDonald’s restaurant near the campus last week had been drinking on the night of the incident and may have instigated the physical confrontation that led to his death, D.C. police said Friday.

The student, Patrick Casey, a 6-foot-4, 280-pound Army veteran of the war in Afghanistan, was knocked down by a shove or a punch and struck his head on the sidewalk just outside the door of the restaurant, in the 1900 block of M Street NW, police said.

In an interview with The Washington Post this week, Casey’s parents said they were told by a witness that their 33-year-old son had been blindsided by a surprise punch while trying to defuse a dispute in which a female friend of his had been pushed.

But a top official of the D.C. police homicide unit contradicted that account Friday.

“From what we’ve been able to establish at this point, Mr. Casey was not just sitting, minding his own business,” Capt. Michael Farish said at a news conference. “He was not just an inactive bystander who decided . . . to come to someone else’s aid. That’s not what our investigation is indicating.”

Farish said detectives have interviewed about a half-dozen people who were involved on both sides of the confrontation as well as other witnesses who were in the restaurant when the altercation occurred, shortly after 2:30 a.m. Sept. 23. He said authorities are not sure whether anyone will be charged in the incident.

“Bits and pieces” of the incident also were recorded by the restaurant’s security video system, Farish said.

“The interviews we’ve conducted thus far with people who were with Mr. Casey [show] he had been drinking that night,” Farish said. He said the D.C. medical examiner’s office, which conducted an autopsy on Casey’s body, has not completed toxicology tests to determine the level of alcohol in his blood.

After Casey arrived at the McDonald’s with two or three friends, he began “interacting with other patrons” in an annoying way, Farish said. “No one has characterized it as looking to pick a fight. He was just being irritating.”

The behavior led to an exchange of words between Casey’s group and a group of about three other people, Farish said. The jawing “escalated to the point that they decided to take it outside. When they started to go outside, a subject in the group [opposing] Mr. Casey’s was either thrown or pushed around.”

The investigation indicates that “the initial push came from, we believe it was Mr. Casey,” Farish said. “It may have been someone who was with him. We’re still ironing that out. That was the initial push that put a subject down on the ground.”

After that push, which occurred near the door, Farish said, “Mr. Casey wouldn’t let anyone leave.” This was followed by some “chest to chest” confrontations among people in the two groups. At some point, the dispute may have spilled through the door and onto the sidewalk immediately in front of the restaurant, Farish said.

“And that was when there was either a punch or a push, resulting in Mr. Casey falling,” Farish said. “I saw some news reports that portrayed it as an assault, that he was beaten. . . . The evidence at this point doesn’t sustain that.”

An ambulance crew called to the scene found Casey unconscious on the sidewalk.

Farish said detectives will continue to review the case and consult with the U.S. attorney’s office before deciding whether, in their view, a serious crime was committed. “What we can clearly establish is the fact that there was some kind of physical contact between one subject and Mr. Casey,” Farish said, “and that would only meet the threshold of a simple assault,” which is a misdemeanor.

The medical examiner’s office, after an autopsy Thursday, ruled that he had died of blunt force trauma to the “back, top area of the head,” Farish said. Although his death was ruled a homicide, Farish noted that such a finding means only that “someone lost his life at the hands of another” and does not necessarily mean that a crime occurred.

Casey, of Clifton Park, N.Y., learned Arabic after joining the Army five years ago, at age 28, and later was sent to Afghanistan. He liked the Army and computers but did not think of either pursuit as a lifelong aspiration, said his mother, Gail Casey.

He returned to the United States in February and enrolled in George Washington’s master’s degree program in international studies.