There were around 3,000 people at the event Wednesday afternoon at the university, where Mr. Kirk, a prominent right-wing political activist, was killed when he was shot in the neck. But only six police officers were present, according to Utah Valley University’s chief of police, Jeff Long, who added that Mr. Kirk also had a private security team that traveled with him.

“You try to get your bases covered, and unfortunately, today, we didn’t,” Mr. Long said during a news conference on Wednesday. “Because of that, we have this tragic incident.”

Questions to the university and to Mr. Kirk’s team about whether concerns had been raised in advance about the site’s security were not immediately answered.

It is not altogether unusual for colleges and universities to host speakers whose appearances stir debate, and public and private schools alike have struggled to balance security costs and logistical demands with their professed commitments to free speech.

“Canceling events must be a last resort to be used only when the campus, despite taking all reasonable steps, believes that it cannot protect the safety of its students, staff and faculty,” the University of California, Berkeley — a college with one of the nation’s richest protest traditions — notes on its website. “Events can never legally be canceled based on the likely offensiveness of the speaker’s message.”

At Utah Valley, a public institution, university policy asserts that the school has the authority “to cancel (or deny pending requests for) an event at any time when it is determined to pose a significant threat to campus health, safety, and security.”

Mr. Kirk spoke on its campus Wednesday from inside the canopy of a small tent, in front of a sloping courtyard framed by ledges and walkways but few barriers. The setting created vantage points that left the crowd, and its speaker, exposed. Even as officers stood watch, students and visitors said, the layout allowed for too many blind spots.

In retrospect, some witnesses said, that turned what had seemed like an inviting campus venue into vulnerable terrain.

“The security detail on the campus regarding this event is something that needs to be looked at,” said Zachary Morris, who attended the event with his 3-year-old daughter. He said in an interview that he was in the back of the crowd, near a grassy break in the courtyard.

Mr. Morris said he had gotten free tickets to the event but that no one had scanned them. Attendees had lined up to question and debate Mr. Kirk, the charismatic founder of the nation’s pre-eminent right-wing youth activist group, on a variety of polarizing topics, including abortion and transgender issues. His Utah Valley appearance was the first stop of a fall tour organized through the political organization he led, Turning Point USA.

From where Mr. Morris stood, he said, it was difficult to hear Mr. Kirk. But when he heard a pop and saw Mr. Kirk jolt, he knew immediately that a gunshot had been fired.

Law enforcement officials have said they recovered what they believe is a rifle used in the shooting. The F.B.I. on Thursday released two images of a “person of interest” investigators are seeking in connection with the shooting, and offered a $100,000 reward for information leading to the arrest of “the individual(s) responsible for the murder of Charlie Kirk.”

In Utah, firearms can generally be bought and carried without a permit. And in May, the state’s lawmakers went further, allowing weapons to be openly carried with a permit by people who are 18 or older on college campuses.

Across the country, many universities have only modest campus security forces, and the costs of protecting events can carry extraordinary price tags.

Berkeley said it and the University of California system had spent close to $4 million over about a month in 2017, according to contemporaneous news accounts, for security at events that included a “Rally Against Hate” and an appearance by the conservative commentator Ben Shapiro. That month also included a multiday event involving the alt-right provocateur Milo Yiannopoulos that was ultimately canceled, but which still cost Berkeley and U.C. close to $2.9 million.

Efforts to pass on security costs to event organizers have sometimes drawn criticism and litigation when their formulas were not seen as content-neutral, or led to cost estimates that appeared excessive.

The Foundation for Individual Rights and Expression, for example, has complained that schools “sometimes hamper student groups hosting outside speakers” through high security fees, a tactic it has denounced as “a practice that directly conflicts with First Amendment standards.”