The Chicago police officer who shot a black teenager last year pleaded not guilty to murder on Tuesday, as Mayor Rahm Emanuel cut short a vacation to return to the city to deal with the fallout from two more fatal police shootings over the weekend.

Meanwhile, protesters demonstrated outside the Cuyahoga County prosecutor's office in Cleveland, a day after a grand jury decided not to charge two white police officers in the 2014 shooting death of Tamir Rice, a black 12-year-old boy who was playing in a park with a toy gun that shoots plastic pellets.

Tensions over race and policing in Chicago and Cleveland come amid intense scrutiny of police killings in the United States over the past 18 months, especially of black men.

Protests have taken place around the country and the issue has fueled a civil rights movement under the name Black Lives Matter.

Chicago Police Officer Jason Van Dyke, who is white, faces six counts of first-degree murder and one count of official misconduct for killing Laquan McDonald, 17, in October 2014.

He pleaded not guilty to all charges at the Cook County criminal court in Chicago.

Van Dyke's lawyer said he may ask for a change of venue.

"We're certainly going to explore every opportunity we have in order for my client to have a fair trial," attorney Daniel Herbert said after the hearing.

The release last month of a video of the shooting, which shows Van Dyke shooting McDonald 16 times, set off a wave of protests and calls for Emanuel's resignation. The mayor fired the police chief and the Justice Department is investigating whether the city's police use lethal force too often, especially against minorities.

Over the weekend, another Chicago police officer fatally shot two black people, setting off more protests, and prompting Emanuel to cut short a family vacation to Cuba.

Bettie Jones, 55, a mother of five, and college student Quintonio LeGrier, 19, were killed on Saturday by an officer responding to a call that LeGrier was threatening his father with a baseball bat. Police said Jones was killed by accident.

Friends and relatives of LeGrier wrapped blue and white balloons around a basketball goal during a candlelight vigil on Tuesday across the street from the high school he graduated from in 2014.

Gathered in the snowy street, they remembered LeGrier as a loving, generous, optimistic person and a good outfielder in baseball.

Gerald Pope, 19, and Monet Booth, 18, were classmates of LeGrier's. Pope said LeGrier gave his last dollar to get home instead of buying a honey bun.

"He was a very humble, optimistic, caring and didn't cause any problems," said Booth. "And to know that my friend, a fellow classmate at Gwendolyn Brooks was gunned down so inhumanely is so disgusting."

Gwendolyn Brooks is one of Chicago's selective enrollment high schools, with competitive admission based on high grades and testing.

Elsewhere in Chicago, about 20 protesters gathered outside the mayor's house on Tuesday, according to CBS Chicago. It was not clear whether Emanuel had yet returned from Cuba as of Tuesday evening. There is also a protest planned at City Hall on Thursday.

While some family members said LeGrier had mental health or emotional issues, others described him as going through college student stress, according to local media reports.

LeGrier excelled in high school while he was brought up by a foster mother after the state removed him from his mother's home because she abused him, the Chicago Sun-Times reported on Tuesday. The paper also said LeGrier faced robbery and assault charges from three incidents since he began attending Northern Illinois University in DeKalb, 65 miles west of Chicago.

LeGrier's father, Antonio LeGrier, has sued the city for wrongful death and for false arrest, saying he was detained and interrogated by the police after the shooting and not allowed to stay with his dying son.

Antonio LeGrier told CNN on Tuesday that the officer was male and was white or Hispanic, and that he knew he had made a mistake after the shooting and exclaimed, "I can't believe it. I thought he was coming at me with that bat," and "F--- no, no."

In Cleveland, about 75 protesters unsatisfied with the grand jury's decision in the Rice case listened to speeches outside the prosecutor's office. They then marched through downtown Cleveland chanting "No justice, no peace, no racist police." The demonstration was peaceful and no arrests were reported.

Cleveland police will review the fatal shooting of Rice from start to finish to determine if the two officers involved or others should face disciplinary action, officials said on Tuesday.

(Additional reporting by Kim Palmer in Cleveland and Mary Wisniewski and Dave McKinney in Chicago; Writing by Fiona Ortiz; Editing by Jeffrey Benkoe, Bill Rigby and Kim Coghill)