Chicago mass shooting that left four dead and four injured was carried out by two people who shot all but one victim in the head execution-style

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A Mass Shooting that left four people dead and four seriously injured in Chicago's Southside was carried out by two gunmen who shot all but one of the victims in the head execution-style, police say.  

Police received a call about shots fired from people on the second floor of the house at about 5.45am Tuesday and when they arrived they found four people dead in various rooms. 

Citing a preliminary report, Chicago police spokesman Steve Rusanov said that someone broke into the home some time before 5.40am on Tuesday and started shooting. 

It marked Chicago's third mass shooting in the span of a week as the US continues to battle a harrowing surge in gun violence.  

Denise Mathis, 32, Rantanya Rogers, 28, Blake Lee, 34, and Shermetria Williams, 19, were killed in Tuesday's shooting. The victims are pictured above from left to right

Police received a call about shots fired from people on the second floor of the house at about 5:45 am and when they arrived they found four people dead in various rooms

Police initially said the shooting broke out after an argument in the home and there were two volleys of gunshots, adding there were no signs of forced entry.

All of the victims had been shot in the head, as had three of the victims who survived, with the remaining surviving victim suffering a gunshot wound to the back. 

Friends and family are mourning the loss of the victims, who had gotten together for a birthday party in the home.

One of the victims, Denise Mathis, 32, was a mother of five who had just taken her children to Six Flags over the weekend.

Mathis' family said she was a devoted mother.

'She was a good person — a free-spirited person,' her cousin Vickie Smith told the Sun-Times. 'She loved her family.'

Also killed in the shooting was 19-year-old Shermetria Williams.

The mother of a 2-year-old daughter was set to graduate from high school the same day she was killed.

Her father Demetrius Williams told the Sun-Times he was at home putting on a shirt and tie for her ceremony when he heard she had been killed.

'This is unbelievable — a massacre,' Williams said at the crime scene as he held the ticket for his daughter's graduation. 'Why? Why did this have to happen?'

Back at her home there were red roses and balloons that said 'Congratulations,' the Sun-Times reported.

Ratanya Aryiel Rogers, 28, was a mother of a young boy who was the birthday girl celebrating her 28th birthday.

Rogers was waiting for a ride home when the gunfire began, the Sun-Times reported.

The fourth victim was 34-year-old Blake Lee, who lived in the home and did odd jobs in the neighborhood, the Sun-Times reported.

Lee's uncle Raheem Hall said he warned his nephew to 'stay away from the wrong crowd.'

'He was a good guy,' Hall added. 'He did no harm to no one. He was just trying to live his life as an ordinary guy.'

Friends and family are mourning the loss of the victims, who had gotten together for a birthday party in the home

All of the victims had been shot in the head, as had three of the victims who survived, with the other surviving victim shot in the back

The killings were among recent massing shootings in Chicago and elsewhere in the country that have prompted fears about a spike in U.S. gun violence heading into the summer.

Days before the a mass shooting in Chicago left a woman dead and nine adults injured when two suspects walked up to a crowd gathered on the sidewalk and opened fire just after 2 a.m. on Saturday, ABC 7 Chicago reported.  

Tuesdays massacre was only the first mass shooting that day- later that afternoon five people were wounded in a shooting in West Garfield Park that left four in good condition and one man in critical condition, Fox 32 reported.  

The shooting at West Garfield Park was the fourth mass shooting in Chicago in just over a week.  

The medical examiner's office reported that nearly 300 of the 390 homicides in Cook County so far this year have taken place in Chicago, according to Fox 32.

Which is down from the 342 the county had recorded during the same period last year. 

At a news conference on Tuesday Chicago Mayor Lori Lightfoot pleaded for help from the federal government, calling for a 'multi-jurisdictional, national solution to this horrible plague of gun violence.'

'This is a national problem,' she said. 'Cities individually cannot tackle this problem. We just cannot. In Chicago, we've done absolutely everything possible and we need help from the federal government.'

A database compiled by The Associated Press, USA Today and Northeastern University that tracks mass killings - defined as four or more dead, not including the perpetrator - showed that Tuesday´s shooting in Chicago was the 18th mass killing, of which 17 were shootings, this year in the U.S.