CHICAGO (CBS) — Through the end of March, murders and shootings were up in Chicago, compared to the same time last year, but police said overall crime is down in the city.

Chicago Police said there were 18 more murders and 107 more shooting incidents in the first quarter of 2015 than the first quarter of 2014, when the city had its fewest number of murders for the entire year since 1965.

However, police said overall crime was down 5 percent in the first three months of 2015, with 623 fewer overall crimes. Police also said officers have seized more than 1,500 illegal guns so far this year, a 22 percent increase over the same period last year; and have made 145 more arrests for illegal gun possession, an increase of about 40 percent.

Police Supt. Garry McCarthy said the number of illegal guns on the streets is a major factor in the rise in shootings and murders.

“The most important thing that I’m seeing in what’s happening here today is something that we talk about all the time. You’ve heard me say it over and over again. We are a city that takes more guns off the street than any police department in the country,” he said. “In 2013, we took seven guns for every one that the New York City Police Department took of the street; and 3-to-1 to Los Angeles.”

McCarthy said, of the more than 500 gun arrests so far this year, 55 percent of the defendants already are back on the street, including two who were arrested and released a second time.

“Until something changes with those gun laws, until such time that people stop carrying guns – because there’ a sanction, criminally, rather than a sanction of a rival gang member finding you without a gun – we’re going to have a problem,” he said.

Crime has been a major topic in the race for mayor. Challenger Jesus “Chuy” Garcia has vowed to hire 1,000 additional police officers – as Rahm Emanuel did when he ran for mayor four years ago – but Mayor Emanuel has said the city can’t afford that, and that placing more police officers on overtime is a more affordable option, as it does not increase pension or health insurance costs.