The New York Police Department has launched its internal investigation into officers' actions in the apparent chokehold death of Eric Garner and it should be completed in three to four months, Police Commissioner William Bratton said on national television Sunday.

Bratton vigorously defended Mayor Bill de Blasio against criticism from Police Benevolent Association president Patrick Lynch, who had said the mayor threw police officers "under the bus" in comments de Blasio made after a Staten Island grand jury decision last week not to indict an NYPD police officer in Garner's July 17 death.

"This is a mayor that has been very, very supportive of equipping the police to deal with many of the issues this city is facing," Bratton said on CBS' "Face the Nation." "He's a progressive. He's certain he wants police to police constitutionally, compassionately, respectfully, which is why he's hired me, because we're both of a shared mind on that issue."

While Lynch's remark "may reflect" the PBA leader's attitude, Bratton said, "We have a very strong difference of opinion on that comment."

Lynch's criticism of de Blasio was in response to some of the mayor's remarks at a news conference after the Garner grand jury's report. De Blasio spoke in personal terms on how he and his wife have to talk to their teenage son, Dante, who is biracial, about "how to take special care with any encounter he may have with police officers."

Sunday, Bratton said the department's internal affairs investigators on Friday began interviewing officers involved when the Staten Island resident was handcuffed and taken down on a sidewalk. If the department advocate, who is a prosecutor, finds grounds for violation of NYPD rules, a trial will be held. The trial judge will make a finding and report it to Bratton, who will make the final decision on the fate of Officer Daniel Pantaleo, he said.

Garner, 43, died after the confrontation with Pantaleo and other officers while being arrested on suspicion of selling loose, untaxed cigarettes.

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Bratton, asked Sunday how he felt watching the cellphone video of the arrest, in which Garner says, "I can't breathe" 11 times, said: "I don't think that anyone that watches that video is not disturbed by what they saw. Policing involving use of force, it always looks awful. We have an expression -- lawful but awful."

Last night, demonstrators voiced their frustrations for a fifth day, with protests inside Grand Central Terminal, Herald Square department stores and in Times Square.

Earlier Sunday, on NBC's "Meet the Press," the Rev. Al Sharpton said a rally will be held on Saturday in the nation's capital in commemoration of Garner and other unarmed black men killed by police. Sharpton who appeared on the show with Esaw Garner, the widow of Eric Garner, said his National Action Network will push for congressional hearings and legislation.

"The Congress needs to not only do hearings, we need to deal with the jurisdictional threshold of how do we make a federal case? How will she get her day in court?" Sharpton said, referring to Esaw Garner.

"It's going to be able to move the jurisdictional threshold, which Congress can do. Congress needs to put money into Justice Department investigations in these cases. We gotta bring protests to where it goes, the legislation," Sharpton said. "Otherwise, we'll be back here again."

Sharpton, asked to react to comments made by Lynch that Garner should not have resisted arrest, said: "To blame the victim, the insensitivity of that is striking."

Garner's death occurred about three weeks before the shooting death of Michael Brown, 18, an unarmed black man, by Officer Darren Wilson in Ferguson, Missouri, which set off days of violent protests and looting there. Last month, a Missouri grand jury declined to charge Wilson, which sparked more violence.

De Blasio, on "This Week" with George Stephanopoulos on Sunday, said he will continue to push policies that improve the treatment of blacks by police officers.

"There's that fear that there could be that one moment of misunderstanding with a young man of color and that young man will never come back," he said.

He reiterated his stance, born of his own talks with his son, about the fear of the police by parents of young men of color.

"What parents have done for decades, who have children of color, especially young men of color, is train them to be very careful when they have an encounter with a police officer," he said. "It's different for a white child. That's just the reality in this country."

With David M. Schwartz