CHICAGO (CBS) — Police are preparing for a busy holiday weekend, and they will be working longer hours to prevent violence and ensure a safe celebration.

Thousands of police officers will work extra shifts to avoid a repeat of last year’s murder wave, when nine people were killed and more than 60 were shot.

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Chicago police officers will work 12 hour shifts Friday through Monday.

All will be in uniform.

Supt. Garry McCarthy said: “In general, crime, violent crime in particular, is highest on Friday and Saturday from 6 p.m. to 8 p.m. to about 2 a.m. to 4 a.m.”

The shootings have already started–just overnight four people were shot in three incidents

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A 46-year-old man was killed on 92nd Street and Ashland as he and a woman were walking in an alley.

Police say someone fired shots from a passing van.

The woman was also shot.

On Thursday, four people died seven others injured from various shootings across the city.

Across the country, there will be tighter security because of the possible threats of terrorism.

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McCarthy said there’s no specific threat to Chicago.