Chicago Mayor Rahm Emanuel, right, and police superintendent Garry McCarthy, second from left, held a news event last month. Emanuel announced Tuesday that he had asked McCarthy to resign. (EPA/Tannen Maury)

Gun control advocates are losing a well-placed and vocal ally in Garry McCarthy, the Chicago police superintendent fired Tuesday over the department's response to a police officer's fatal shooting of a black teenager.

As Chicago's top cop since 2011, McCarthy presided over a city with one of the highest municipal murder rates in the country and made efforts to control the city's black market for guns. In October, McCarthy announced he was assigning detectives to trace every gun recovered in some districts, to help identify people importing weapons for sale on Chicago's black market.

McCarthy also called for stricter national gun control laws, supporting mandatory background checks for all gun purchases, including private sales. And he argued that felons caught illegally carrying guns should serve longer sentences.

"We can point to, right now, in 2015, at least 150 shootings or murders that would not have occurred if we had stricter penalties for gun possession," McCarthy recently told WLS-TV in Chicago. "One hundred and fifty. That's a lot of people getting bullets in them."

Mayor Rahm Emanuel asked McCarthy to resign after the city released video showing an officer fatally shooting 17-year-old Laquan McDonald in the back. The officer, Jason Van Dyke, was charged with first-degree murder last week, and aldermen, pundits and activists called for McCarthy's termination.

[Read more: People are getting shot by toddlers on a weekly basis this year]

The large number of guns on Chicago streets have led to a murder rate higher than the country's two largest cities, Los Angeles and New York. According to a 2014 report, officers seized 7,624 guns in Chicago in 2012, or 277 guns per every 100,000 people living in the city. For the Los Angeles Police Department, that figure was 122 guns, and in New York, it was just 39. The discrepancy suggests that far more people in Chicago bear arms.

McCarthy often voiced frustration that lawmakers did not do more to help him keep guns out of the city. Between 2009 and 2013, more than 60 percent of guns used to commit crimes that Chicago police recovered were first sold in other states where laws on guns are more lax. Almost half of that number came from Indiana, and many of the rest were purchased in Mississippi and Wisconsin.

Homicide rates were volatile during McCarthy's tenure, ranging from as many as 500 in 2012 to a low of 407 last year. There have been 439 homicides in Chicago so far this year.

"I don't think anyone can blame Garry for not trying," said Jim Bueermann, president of the D.C.-based Police Foundation. "He spoke eloquently about the need for us to get smarter about guns in this country."

"We have a national gun market,"said Harold Pollack, who studies crime and public health at the University of Chicago, "and it's very hard for any one city to get a handle on it."

Pollack and his colleagues recently interviewed inmates in Cook County Jail about where they found their guns. In some cases, criminal organizations ship guns in bulk from outside the city. In others, a gun originally bought legally ends up in criminal hands after a gun owner sells his weapon second-hand.

"The typical gun that's used in a crime has passed through many hands," Pollack said.

A large body of evidence suggests the presence of firearms makes homicide more likely. Researchers at the Harvard School of Public Health have found that in the states where more people own guns, more people are killed -- even after accounting for the varying numbers of people living in poverty or in large cities, how much alcohol is consumed, and overall violent crime rates in each state. Research comparing homicide rates in the United States and in other countries has confirmed that finding.

[Read more: What liberals don’t want to admit about gun control]

Bueermann, who served as chief of police in Redlands, Calif., said that guns allow ordinary violent disputes to escalate quickly. Likewise, criminals who mean to do harm have a hard time finding equally lethal weapons when they can't purchase a gun or find someone who will loan them one. A knife wound is about eight times less likely to be lethal than a gunshot wound, according to one study conducted on trauma patients in emergency rooms in Albuquerque, N.M.

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11 essential facts about guns and mass shootings in America

There are now more guns than people in the United States

The average gun owner now owns 8 guns — double what it used to be