Story highlights Police superintendent draws a distinction between protesters and criminals

Obama says police did a "great job under some significant pressure"

Protesters rally outside the Chicago campaign headquarters of Obama

Dozens were injured in clashes between police and protesters Sunday

Protesters rallied outside the Chicago campaign headquarters of President Barack Obama on Monday on the last day of the two-day NATO summit.

The peaceful nature of the demonstration came in stark contrast to violent clashes that left protesters and eight police officers injured a day before.

"NATO has to go. Everywhere they go, this is the result -- violence against innocents, violence in the service of the international 1%," said Joe Iosbaker, an activist.

"We are here to demand accountability, and we're not just talking about the rank and file cops who did the swinging and split skulls. We're talking about (Chicago) Mayor (Rahm) Emanuel and (Chicago) Police Superintendent (Garry) McCarthy," he said.

Earlier in the day, protesters chanted and tossed paper airplanes as they protested Boeing Corp.'s role as a defense contractor.

"These are peaceful protesters. That's what we expected," said superintendent McCarthy. Later in the day, he drew a distinction between protesters and criminals.

"Yesterday was not a clash between protesters and police. That was a clash between criminals and police," he told CNN. "The news isn't what happened. The news is what did not happen."

By early afternoon, protesters had moved on from the heavily guarded Boeing building, where some windows had been covered in anticipation of possible violence.

"It's kind of a celebration," protester Blaise Sewell said. "We effectively shut down Boeing with a Facebook event."

While McCarthy said officers behaved admirably in the face of attacks by protesters Sunday, the Chicago chapter of the National Lawyers Guild accused police, in a statement, of "indiscriminate violence."

"Police completely overreacted to protesters approaching the security perimeter and unleashed a violent attack on them without an ability to disperse," attorney Sarah Gelsomino of the People's Law Office said in the guild statement.

Protesters suffered serious injuries, including broken bones, busted lips and concussions, she said at a Monday rally. The guild has close to 60 accounts of police brutality, Gelsomino said.

Security remained tight in Chicago as the summit wound down. Commuters faced a more difficult trip with the closure of 25 stops on the city's Metra train lines, which had been planned earlier. The city's iconic Lake Shore Drive was also to remain closed through much of downtown, city officials said.

Speaking inside the the NATO meeting, President Barack Obama thanked the people of Chicago for putting up with the traffic and also the city's mayor and its police force for their work, which he said was done under "some significant pressure and a lot of scrutiny."

"This is part of what NATO defends -- is free speech and freedom of assembly," he said.

A day earlier, police clashed with protesters at the end of a march just blocks from the NATO summit after a they refused police orders to disperse and began pushing against a line of officers clad in riot gear.

A video from CNN affiliate WLS showed protesters, some with bloodied faces, struggling against the officers, some of whom struck the demonstrators with batons.

The confrontation led to a two-hour standoff between police and protesters.

Occupy Chicago said dozens were injured in the clashes, though fewer than a dozen protesters were treated at area hospitals, officials said.

McCarthy said Monday that eight officers had been injured, including one who was hospitalized for exhaustion and another who was stabbed in the leg but went back on duty hours later.

Police said they arrested at least 45 people Sunday. The National Lawyers Guild estimated 60 arrests Sunday and more than 100 since the summit began.

On Sunday, McCarthy said officers responded after protesters assaulted them, and "the finger should be pointed at the people who assaulted the cops."

On Monday, he said protesters were largely peaceful and blamed Sunday's violence on a group of protesters intent on breaking the law. While police want to protect people exercising free speech rights, he said, they cannot tolerate illegal acts.

Police spokeswoman Melissa Stratton also said Monday that some protesters had splashed themselves with fake blood before returning to the protest lines.

While some protesters accused police of brutality in Sunday's confrontations, Illinois Lt. Gov. Sheila Simon said Monday that police seemed to be doing a good job.

"I think for the most part, they have been doing a fantastic job of making sure that people are protected and free speech rights are protected as well," she said. "It's a tough balance to get, but I think they are doing a good job."