Barack Obama called for calm when he condemned the shooting of two uniformed police officers in New York while they sat in their patrol car.
Speaking after the murders of Rafael Ramos and Wenjian Liu - with suspect Ismaaiyl Brinsley understood to have killed himself afterwards - the US president said:
I unconditionally condemn today's murder of two police officers in New York City. Two brave men won't be going home to their loved ones tonight, and for that, there is no justification. The officers who serve and protect our communities risk their own safety for ours every single day - and they deserve our respect and gratitude every single day.
Tonight, I ask people to reject violence and words that harm, and turn to words that heal - prayer, patient dialogue, and sympathy for the friends and family of the fallen.
But one person who didn't seem to agree with Obama's sentiment was Hollwood actor James Woods, who returned to Twitter after an absence of several months.
In a series of tweets sent from his verified account the 67-year-old laid into civil rights activist Rev Al Sharpton and New York mayor Bill DeBlasio, culminating in the posting of this image:
Before shooting the two officers, Brinsley had suggested he was planning on killing members of the police over the decision of a grand jury not to indict a white officer who put Eric Garner, a black man, in an illegal chokehold that resulted in his death.
That itself followed a separate grand jury clearing another white police officer over the fatal shooting of black teenager Michael Brown.
Writing in the New York Daily News, Rev Sharpton said he had spoken to the families of Garner and Brown and that they were all "outraged and saddened by the deaths of these police officers".
"Any use of the names of Eric Garner and Michael Brown, in connection with any violence or killing of police, is reprehensible and against the pursuit of justice in both cases," he added.