NEW YORK -- Authorities on Monday said they were trying to finalize the whereabouts of the "deeply troubled career criminal" during the few hours before he executed two New York City police officers in their patrol car over the weekend.
Chief of Detectives Robert Boyce said that police had established the whereabouts of Ismaaiyl Brinsley up until about noon on Saturday but could not account for where he was until 2:30 p.m. Boyce said Brinsley was seen in surveillance footage at Atlantic Terminal, holding a bag that authorities believe was covering the gun used to kill the officers.
Police Commissioner William Bratton said that police have received some copycat threats but none have proved credible. He said that Brinsley "acted alone."
Boyce said police had recovered Brinsley's cellphone in Baltimore, which contains video of the 28-year-old attending a protest in Union Square Park earlier this month. He said police had also analyzed 119 social media messages posted by Brinsley, some of which contained anti-government messages.
New York City Mayor Bill de Blasio called for a temporary halt to protests over police conduct as he faced a widening rift with a force preparing Christmastime burials for two of its own and decrying the demonstrations as a factor in the officers' cold-blooded executions.
"I think it's important that, regardless of people's viewpoints, that everyone step back," de Blasio said. "I think it's a time for everyone to put aside political debates, put aside protests, put aside all of the things that we will talk about in all due time."
De Blasio's relations with the city's police unions have tumbled to an extraordinary new low - one not experienced by a mayor in the nation's largest city in more than a generation - in the aftermath of Saturday's shooting in which the gunman claimed was retaliation for the deaths of black men at the hands of white police. In a display of defiance, dozens of police officers turned their backs to de Blasio at the hospital where the officers died, and union leaders said the mayor had "blood on his hands" for enabling the protesters who have swept the streets of New York this month since a grand jury declined to indict an officer in the chokehold death of Eric Garner.
De Blasio, in his first extensive remarks since the killings, called for "everyone to put aside political debates, put aside protests, put aside all of the things that we will talk about in all due time."
Officers Wenjian Liu and Rafael Ramos were ambushed Saturday afternoon by a 28-year-old who vowed in an Instagram post that he would put "wings on pigs." Brinsley was black; the slain New York Police Department officers were Hispanic and Asian.
The killings came as police nationwide are being criticized following Garner's death and 18-year-old Michael Brown's fatal shooting in Ferguson, Missouri. Protests erupted after grand juries declined to charge officers in either case.
On Monday, a prosecutor said a white Milwaukee police officer who was fired after he fatally shot a mentally ill black man in April won't face criminal charges. Lawyers for the slain man's family urged any protesters there to be peaceful.
De Blasio said it was time to focus on the officers' grieving families. He and Bratton met with them earlier Monday.
"There's a lot of pain. It's so hard to make sense of it - how one deeply troubled, violent individual could do this to these good families," a somber de Blasio said. "And I think it's a time for everyone to take stock that there are things that unite us, there are things that we hold dear as New Yorkers, as Americans."
Investigators are trying to determine if Brinsley had taken part in any protests, or simply latched onto the cause for the final act in a violent rampage. He started off Saturday in Baltimore, shooting his ex-girlfriend in the stomach before coming to New York and killing the officers. He then ran into a nearby subway station and killed himself.
The police unions blame de Blasio for fostering an anti-police sentiment. Patrolmen's Benevolent Association President Patrick Lynch declaring that there was "blood on the hands" on the "steps of City Hall and the office of the mayor."
Sergeants Benevolent Associations head Edward Mullins refused to back down from that stance, saying in an interview Monday that "the mayor has turned his back on us - he got elected on his campaign of attacking the police all along."
That link - strenuously denied by the de Blasio administration - was given some credence by Police Commissioner William Bratton on Monday. In an interview with NBC, Bratton said "what's quite apparent, obvious, is that the target of these two police officers was a direct spinoff of this issue of these demonstrations."
Even Bratton, who has steadfastly praised de Blasio, conceded that the mayor was on shaky footing with some in the NYPD. When asked on NBC's "Today" show if the mayor had lost the force's trust and confidence, Bratton said, "I think he's lost it with some officers."
Philadelphia Police Commissioner Charles Ramsey said Monday on "CBS This Morning" that the snipping may have gone too far.
"I think right now everyone should just focus on the families of the two slain officers, put them away with the dignity and the respect that they certainly deserve," Ramsey said. "The rest of this can be sorted out at a later time, but right now everyone needs to lower the volume a little bit on the rhetoric because we're just in a very, very volatile environment right now."
Meanwhile, big-city police departments and union leaders around the country were warning the rank and file to wear bulletproof vests and avoid making inflammatory posts on social media.
A union-generated message at the 35,000-officer NYPD warned officers that they should respond to every radio call with two cars - "no matter what the opinion of the patrol supervisor" - and not make arrests "unless absolutely necessary." The president of the detectives' union told members in a letter to work in threes when out on the street, wear bulletproof vests and keep aware of their surroundings. At the same time, a memo from an NYPD chief asked officers to limit their comments "via all venues, including social media, to expressions of sorrow and condolence."
One directive warned officers in Newark, New Jersey, not to patrol alone and to avoid confrontation. In Philadelphia, Police Commissioner Charles Ramsey urged protest leaders to "call for calm and not let this escalate any further." Boston's police commissioner said officers there were on alert.
Officials in New York investigated at least a dozen threats against police since the shootings, and one man was arrested at a Manhattan precinct after he walked in and said: "If I punch you in the face, how much time will I get?" and refused to leave.