Days after the defense raised the prospect that a fatal punch to a random robbery victim could have been thrown by someone else — a someone authorities can no longer charge with that act — prosecutors have dismissed a murder case against the suspect they thought had landed the telling blow on Hennepin Avenue after bar closing time.

“Witness issues” forced prosecutors on Wednesday to drop the murder charge against Ethan Z. Hayes, 34, currently imprisoned in Stillwater for one more week on an unrelated assault conviction. Hayes had been charged in Hennepin County District Court with second-degree murder in the death of Adrian Hernandez, 44, of Minneapolis, on Aug. 22, 2013.

Hayes was accused of being the person who punched Hernandez in the face, sending him to the pavement, where he hit his head and suffered a fatal brain injury.

Guilty pleas to second-degree murder have been made by accomplices Andrew M. Myers, 25, formerly of St. Louis Park, and Vereice D. Washington, 23, of Brooklyn Center. Myers was given a four-year sentence. Washington is to be sentenced next week.

The dismissal leaves no one charged with inflicting the fatal blow to Hernandez, well-known in the Latino community as a Mexican folk dancer and founder of a troupe called Mexico Lindo.

In filing for the dismissal, Assistant County Attorney Christopher Freeman explained, “At this time, due to witness issues, the state cannot proceed and prove the case beyond a reasonable doubt.”

The document offered no elaboration. However, a defense filing last week notified the court that it would seek to undermine testimony from the accomplices. Most notably, the filing suggests it was more likely to have been Myers who killed Hernandez, based on Myers’ convictions of two similar crimes in 2011 and 2014, also downtown on Hennepin Avenue. In each case, Myers punched a robbery victim. Both people survived.

Because Myers has already been tried and convicted in the robbery and killing of Hernandez, he cannot be charged with being the person who threw the fatal punch. That would be double jeopardy.

“As sometimes happens in cases, the cooperation of witnesses can ebb and flow,” said Chuck Laszewski, spokesman for the Hennepin County attorney’s office.

It was a year after the killing when Washington viewed video surveillance from the scene of the attack and told police that Hayes was the man who punched Hernandez.

Police said Washington saw an intoxicated Hernandez near Augie’s bar on Hennepin Avenue. Washington asked to borrow Hernandez’s cellphone, but Hernandez refused. Washington kept walking near Hernandez and was joined by Myers and the man Washington later identified as Hayes. As they walked south, the stalkers plotted to rob Hernandez.

When they reached Hennepin and 10th Street, according to police, the fatal punch was thrown. Hernandez fell, striking his head on the concrete. Washington went through his pockets, stole his cellphone and the men ran away.