Faced with two massive law enforcement situations -- security for the Grammy Awards and a manhunt for an ex-cop wanted in three slayings -- the Los Angeles Police Department declared a tactical alert Sunday night.

The LAPD did not detail its Grammy security arrangements, but the department regularly sends a large contingent of officers to awards shows.

This year, the Grammys occurred on the fifth day of a manhunt for Christopher Dorner, who is suspected of killing an Irvine couple and a Riverside police officer.

The tactical alert came the same day that Los Angeles Mayor Antonio Villaraigosa announced a $1-million reward for information leading to Dorner's capture.

“We will not tolerate anyone undermining the security of this community,” Villaraigosa said at a news conference at LAPD headquarters downtown. “We will not tolerate this reign of terror.”

Dorner allegedly carried out the slayings as part of a vengeful campaign sparked by his 2009 dismissal from the Los Angeles Police Department, authorities said.

Sunday's tactical alert was declared shortly after 2 p.m. In a tactical alert, officers can be held over on their shifts and do not respond to low-priority radio calls.

Officials hope the huge reward will give police the break they've been waiting for.

Police Chief Charlie Beck said the reward was "the largest local reward ever offered to our knowledge." The reason for such a significant reward, Beck said, was "not about capturing a fleeing suspect, but about preventing another crime, likely another murder."

TIMELINE: Manhunt for ex-LAPD officer

"This is an act of domestic terrorism," Beck said of those killed and allegedly targeted by Dorner. "He has targeted those we entrust to protect the public."

A massive manhunt for Dorner began last week after the 33-year-old former officer and Navy veteran allegedly began a deadly campaign that has left an Irvine couple and a Riverside police officer dead.

The city of Los Angeles, law enforcement organizations, private groups and anonymous donors have all contributed to the reward fund, according to law enforcement sources familiar with the investigation.

INTERACTIVE MAP: Searching for suspected shooter

Los Angeles County Supervisors Michael D. Antonovich and Mark Ridley-Thomas are expected to ask the Board of Supervisors on Tuesday to contribute $100,000 to the fund, according to Tony Bell, an Antonovich spokesman.

In addition to Los Angeles officials, representatives from the Riverside and Irvine police departments and the FBI and U.S. Marshals Service attended the news conference.

The frustrating search for Dorner has gone from Riverside to Corona to Big Bear to Point Loma in San Diego. There have been numerous false starts, but officials say the heightened publicity has not brought them closer to making an arrest.

PHOTOS: Manhunt for ex-LAPD officer

Dorner's Nissan Titan pickup was found Thursday morning engulfed in flames on a mountain road in the Big Bear area, and law enforcement officials have since focused their search efforts there.

Officials said Sunday the search in Big Bear was winding down.

On Saturday, Beck announced that he was reopening the investigation into the firing of Dorner from the Police Department.

Beck said he was reopening the investigation "not to appease a murderer" but to assure the public his department is fair and transparent. He said he wanted to protect an "increasingly positive relationship with the community" that the LAPD has developed over the last few years.

Meanwhile, more information was released about the Riverside police officer killed Thursday.

Michael Crain was an 11-year veteran of the department.

Crain, 34, was killed when he and his partner were allegedly fired upon by Dorner.

“While God is quick to forgive, he does demand justice, and there will be a day of reckoning," said Riverside Mayor Rusty Baker, who called Crain's death "senseless."

TIMELINE: Manhunt for ex-LAPD officer

Crain served two tours in Kuwait as a rifleman in the 15th Marine Expeditionary Unit, 3rd Battalion 1st Marines, according to a news release. He leaves behind his wife, a 10-year-old son and a 4-year-old daughter.

Funeral services are scheduled for 10:30 a.m. Wednesday at Grove Community Church in Riverside.

Authorities say Dorner ambushed Crain and his 27-year-old partner when they were stopped at a red light at the intersection of Arlington and Magnolia avenues in Riverside early Thursday morning. Dorner then allegedly fled.

Crain's partner, who was also struck by gunfire, is expected to survive.

ALSO:

Ex-girlfriend called Dorner "emotionally disturbed"

Dorner manhunt: Officers opened fire on mother, daughter

Dorner had history of complaints against fellow LAPD officers

-- Andrew Blankstein and Wesley Lowrey

Photo: Police block a street near Staples Center in advance of the Grammy Awards. Credit: Frederic J. Brown / AFP/Getty Images