Minneapolis live updates: ICE arrest powers expanded, memo says

The Minnesota National Guard has been activated for operations securing the Whipple Federal Building and the site of this morning's shooting, "providing depth and capability to state and local law enforcement," Army Maj. Andrea Tsuchiya, a spokesperson for the Minnesota National Guard, said.

Minnesota Guardsmen have been on standby since Jan. 8. Frey said members from those of other agencies will wear reflective vests to be more visible.

"Our community is tired, our officers are tired, our businesses are tired and this additional support is necessary," Minneapolis Mayor Jacob Frey said at a news conference.

-ABC News' Christopher Boccia

The 37-year-old American citizen killed by a Border Patrol agent was identified as Alex Pretti, according to the  AFGE Professional Local 3669, which represents professional employees affiliated with the Minneapolis VA Health Care System.

"[A] member of our union lost their life today, and that alone is devastating. Our hearts are heavy, and we are deeply stricken by this tragedy that has befallen one of our own," the union said.

The American Nurses Association also released a statement saying it is "deeply disturbed" by the Pretti's death. 

The ANA is calling for a "a full, unencumbered investigation" and urged findings to be shared with Pretti's family and the public. 

The Associated Press reported that Pretti worked as an ICU nurse.

Drew Evans, the superintendent of the Minnesota Bureau of Criminal Apprehension, said that the Department of Homeland Security denied his agents from accessing the crime scene after the shooting

Evans said he obtained a search warrant from a judge.

"We had a signed warrant and we were stilled denied access," he said.

Evans said he has never had a federal agency deny local investigators access to a crime scene in his over 20 years of experience.

The federal agents left the scene, but due to security concerns the BCA team could not collect evidence from the scene. DHS is running the investigation, according to Evans.

Evans, however, said his agency is talking to witnesses, gathering video and other evidence from outside of the scene.

The NBA announced Saturday that the matchup between the Golden State Warriors and the Minnesota Timberwolves, which was scheduled to take place at the Target Center in Minneapolis, was postponed to Sunday.

"The decision was made to prioritize the safety and security of the Minneapolis community," the league said in a statement.