CHICAGO (WLS) -- At least 13 people were killed and another 52 wounded in shootings in Chicago over the Labor Day weekend, Chicago police said.Police were frustrated in the wake of the violent weekend, which is the most violent holiday weekend of 2016 in the city. There were no fatal shootings on Saturday, but on Sunday four people were killed and on Monday nine people were killed in seven shootings on the West and South sides.Chicago police spokesman Anthony Guglielmi said Tuesday that police have persons of interest in custody for three of the seven fatal shootings Monday. Charges are likely, police said.Police Superintendent Eddie Johnson said the majority of the victims are on the police department's list of known criminals, a point he's stressed repeatedly over the past several months."We need to enact tougher penalties so that these individuals know that their actions will not go without consequences. Until then, you will keep hearing the same thing from me and keep seeing the same results on the streets," Johnson said at a press conference.Johnson said despite the police union's effort to get officers to refuse overtime during the holiday, manpower was not an issue in the surge in violence Monday.Near 53rd and Sangamon streets, a pregnant woman and her boyfriend were shot in the middle of the afternoon Monday. Police said two gunmen approached on foot from a gangway between homes and opened fire. Crystal Meyers, 23, was shot in the stomach and transported to Stroger Hospital in serious condition. Her boyfriend, Albert Moore, was shot and is also in critical condition at Stroger Hospital."I was upstairs in the room when I heard the shots. When I come downstairs it was done, the shots was done already, and everything. And she was laying down there," said Tyler Thomas, victim's grandfather.More than a dozen shots were fired at the couple; nine hit Moore and five hit Meyers. Meyers delivered her baby via cesarean at Stroger shortly after the shooting. Both mother and baby are stable, while Moore remains in critical condition."It's rough, real rough. Real, real rough," Thomas said.On the West Side, five people were shot, two fatally, late Monday night.Late Monday evening, a man was shot while driving on the Dan Ryan Expressway. The shooting occurred near 83rd Street at about 11:24 p.m., police said. His injuries are described as non-life threatening.About 4 p.m. in Back of the Yards on the South Side, Albertano Medrano was driving in the 4500-block of South Hermitage when three people in a white van began to harass him, authorities said. Medrano kept driving away, and one of the passengers in the white van opened fire, striking him in the head, neck and back. His vehicle then crashed into three other vehicles after he was shot. Medrano, who lived in the 1800-block of West 46th Street, was taken to Stroger Hospital, where he was pronounced dead at 4:30 p.m., police and the medical examiner's office said.Hours earlier in the Brighton Park neighborhood on the Southwest Side, the roommates of a 22-year-old Enrique D. Morales found him dead about 1:30 p.m. on their driveway in the 4500-block of South Whipple, according to police and the medical examiner's office. Morales was shot in the chest and was pronounced dead at the scene at 1:45 p.m. Area Central detectives were conducting a homicide investigation.Monday morning, a man was killed and another wounded in more Englewood violence. David Baldwin, 24, was shot in the head about 9:30 a.m. in the 6800-block of South Emerald and taken to Christ Medical Center in Oak Lawn, where he died at 2:58 p.m., authorities said.About 6:20 a.m. in the South Shore neighborhood, someone walked up to an 80-year-old man in the 2800-block of East 77th Place, exchanged words with the elderly man and then shot him in the face. He died at the scene, according to police, who said the shooter was arrested with charges pending Monday night. The 80-year-old man's name has not been released.Late Sunday in the same neighborhood, two gunmen walked up to a 17-year-old boy about 10:30 p.m. in the 7800-block of South Cornell and shot him in the back. The teen was taken to Northwestern Memorial Hospital, where he later died, police said. His name has not been released.Just after 6 p.m. Sunday, officers responding to a call of more Back of the Yards neighborhood gunfire in the 5200-block of South Sangamon found a 19-year-old man shot multiple times. He was taken to Stroger Hospital, where he was pronounced dead, authorities said. His name has not been released.Less than an hour earlier, a 45-year-old man was killed and a 27-year-old wounded in another Englewood shooting. Robert L. Porter Jr. and the younger man were unloading boxes in an alley in the 6700-block of South Green when someone dressed in black walked up and fired shots, authorities said. Porter, of the 7300 block of South Green, was shot across the torso and chest and taken to Christ Medical Center, where he died at 6:02 p.m. The other man was taken to the same hospital in serious condition with wounds to the chest, back and wrist, police said.The holiday weekend's first fatal shooting happened early Sunday in the Archer Heights neighborhood on the Southwest Side. Juan Pita-Rosas, 32, was standing in an alley with a 22-year-old man shortly after midnight in the 4800 block of South Kildare when they heard gunfire and both felt pain, authorities said. Pita-Rosas, who lived in the 4700 block of South Springfield, was shot in the head and taken to Mount Sinai Hospital, where he was pronounced dead at 1:05 a.m. The younger man suffered gunshot wounds to the arm and chest and later showed up at Holy Cross Hospital in serious condition.During last year's Labor Day weekend, 9 people were killed and 46 others wounded. This year to help combat the crime, Chicago Police Superintendent Eddie Johnson even went out on patrol.