Denver police are investigating whether a string of New Year's Day attacks downtown are linked and whether they are among the random beatings that nationwide have become known as "the knockout game."

Three cases in LoDo around the same time — between 12:30 and 1:30 a.m. Jan. 1 — caught detectives' attention.

In one, two people reported being assaulted by a group of men near 20th and Larimer streets. In another, a man said he was attacked at 16th and Blake streets. The third case was a beating at 20th and Market streets. Each attack involved as many as four suspects, department spokesman Sonny Jackson said.

One victim was seriously injured with a broken jaw. Some are struggling to remember details.

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"In one case, the guys didn't know what happened or when it happened," Jackson said. The department announced the assaults Monday because some of the victims did not come forward immediately.

"These have been kind of trickling in," Jackson said. "In looking at them, we determined there was potentially a pattern."

Detectives don't know if the attacks are part of a nationwide phenomenon known as "the knockout game," in which an assailant assaults a random stranger to knock him out in one punch. The "game" has captured headlines and generated warnings in recent months.

"One of the victims did say he felt like that's what it was," Jackson said. "An assault is frustrating no matter what you call it."

Although the department has surveillance cameras scattered around LoDo, police are seeking video and photos from New Year's Eve revelers who may have witnessed the commotion. The streets likely were crowded, and witnesses may not have realized what they were seeing, Jackson said.

Assaults and robberies have long troubled LoDo during closing time, when thousands of revelers spill out of bars and nightclubs and into the streets.

A person is more likely to be a crime victim between 1 and 3 a.m. in LoDo than in any other part of the city at that time, an analysis of police data shows.

Sadie Gurman: 303-954-1661, sgurman@ denverpost.com or twitter.com/sgurman