New York man charged with murdering police officer Brian Moore
Suspect Demetrius Blackwell walks into court for his arraignment in Queens County Criminal Court in New York, May 3, 2015. REUTERS/Theodore Parisienne/Pool

A New York man accused of shooting a plainclothes police officer last month was charged with first-degree murder on Thursday, in a 12-count indictment that stiffened prior charges after the officer's death.

Demetrius Blackwell, 35, was arrested hours after he allegedly shot New York Police Department officer Brian Moore, 25, in the head after Moore attempted to question him in a middle-class section of the borough of Queens on May 2. Moore died on May 4.

Blackwell was also charged with the attempted murder of Moore's partner, Erik Jansen.

Those charges are in addition to earlier charges of aggravated assault on a police officer, first-degree assault and weapons possession. The aggravated murder charge carries a maximum possible sentence of life in prison without the possibility of parole.

"The defendant's alleged conduct, and his total disregard of the law and authority, clearly demonstrate that he is a serious threat to society," said Queens County District Attorney Richard Brown.

Blackwell will be arraigned in state Supreme Court later on Thursday, Brown said.

Moore's death came at a time of fraught relations between police and minority communities across the United States.

Police killings of unarmed black men in New York, Missouri, South Carolina and elsewhere have provoked months of largely peaceful protests punctuated with bouts of arson and looting. A gunman who in December shot and killed two uniformed New York police officers as they sat in their patrol car in Brooklyn left postings on social media suggesting his attack was an act of revenge for police killings of black men.

Blackwell is black, and Moore was white.

Moore's shooting did not appear to be politically motivated and his funeral last month featured none of the ire seen at ceremonies for the officers killed in Brooklyn, where thousands of New York Police Department officers in uniform turned their backs on Mayor Bill de Blasio, whom police union officials had accused of not adequately supporting officers.