At least four people were killed and 12 others wounded in shootings across Chicago at the start of the Martin Luther King Jr. holiday weekend, officials said.

The victims were killed in separate neighborhoods across the city, police told the Chicago Sun-Times.

The news outlet reported that police didn’t have many clues Sunday morning when Tion Anderson, 18, was found shot to death in a South Side apartment stairwell.

Earlier, the body of a 39-year-old man was discovered in an alley in the Gresham neighborhood on the city's South Side just after midnight Saturday, officials told the paper.

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An hour later, two people were driving in the Little Village neighborhood on the South Side when someone in another vehicle pulled up and opened fire, killing a 19-year-old woman and injuring the male driver.

That same hour, the body of woman with a gunshot wound to the head was found around 1:35 a.m. in the hallway of an apartment building in the city's Avondale neighborhood on the Northwest Side, the paper reported.

Several were also reported injured in a shooting in the West Garfield Park neighborhood, located on the city's West Side.

The violence over the long holiday weekend came nearly a week after Chicago marked the first day of 2019 without any reported gun violence.

Police have said most killings in Chicago are tied to street gangs, with members vying for control of territory or simply retaliating for perceived slights by gang rivals, which these days are typically communicated through social media.

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While homicide numbers dropped in many districts in Chicago in 2018, they went up in several neighborhoods on the city’s South and West Sides. Those areas have been plagued for years by gun and gang-related violence, including Englewood and West Garfield Park.

According to preliminary numbers, homicides in Chicago, the nation’s third-largest city, fell by about 100 in 2018, compared to 2017 — though the total again eclipsed the number of homicides in Los Angeles and New York City combined. Official numbers for 2018 were expected to be released in several weeks, according to the department.

Although the decrease in 2018 was significant, the number of killings in Chicago was higher than the combined total in New York City and Los Angeles -- for at least the third straight year.

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Police in Chicago reported 561 homicides were committed between Jan. 1 and Dec. 31, 2018. That compared to 660 homicides in 2017 and more than 770 in 2016, which marked a 19-year high that put a national spotlight on Chicago’s persistently high rates of gun violence.

Fox News' Frank Miles, Ryan Gaydos and The Associated Press contributed to this report.