On Monday, a gunman opened fire onto an Independence Day parade in Highland Park, Illinois, a suburb of Chicago, killing at least six people and wounding at least 30, causing what one doctor at the scene called "wartime injuries."

Who dies from gunfire in the United States (and how), charted

Details on the mass shooting

According to Highland Park Police Commander Chris O'Neill, the gunman used a "high-powered rifle" to fire from the rooftop of a commercial building onto the parade. O'Neill said the shooter was "very difficult to see" on the rooftop and that the rifle the shooter used was recovered at the scene.

Christopher Covelli, from the Lake County sheriff's office, said the crime was "very random, very intentional," adding that the shooter used an "unsecured" ladder to climb to the rooftop.

Covelli said that "several of the deceased victims" died at the scene and one victim was taken to a hospital and died there. Lake County Coroner Jennifer Banek said the five people killed at the scene were all adults, however information was not available on the sixth victim.

Authorities said a man named as a person of interest was taken into police custody Monday evening.

"It is devastating that a celebration of America was ripped apart by our uniquely American plague," Illinois Gov. J.B. Pritzker (D) said at a news conference. "I'm furious because it does not have to be this way … while we celebrate the Fourth of July just once a year, mass shootings have become a weekly—yes weekly—American tradition."

President Joe Biden on Monday said he and first lady Jill Biden were "shocked by the senseless gun violence that has yet against brough grief to an American community on this Independence Day."

How health care providers responded

David Baum, a doctor, was at the scene of the shooting and treated some of the victims at the scene, saying that some of the dead were "blown up."

"The horrific scene of some of the bodies is unspeakable for the average person," Baum said. "[T]he injuries … that I saw—I never served—but those are wartime injuries," he added. "Those are what are seen in victims of war, not victims at a parade."

Officials at NorthShore University Health System said 38 victims were taken to hospitals via ambulance or other vehicles.

"There's been a lot of different events that have happened in the United States, and this obviously now has hit very close to home. It is a little surreal to have to take care of an event such as this, but all of us have gone through extensive training," said Brigham Temple, medical director of emergency preparedness at NorthShore.  "We go through a number of different programs, training. We practice for these events even though we hope they never happen. So I think our team very admirably handled the situation today."

According to Temple, 25 of the victims taken to the hospital with injuries had sustained gunshot wounds. The injuries varied in severity. "Some of them were minor," Temple said. "Some of them were much more severe."

As of Monday evening, 19 of the victims were released from the hospital and two were still admitted, Temple said. Others were sent to hospitals in Evanston, Glenbrook, and Lake Forest.

Temple added that patients treated at Highland Park Hospital ranged in age from 8 to 85-years-old, and "four or five" of the hospitalized patients were children.

Highland Park Hospital went on alert immediately following the shooting and, within 30 minutes, brought in 20 additional doctors and many nurses and support staff to help treat patients, CBS News reports.

"There was a child who was shot and injured here that was too unstable to transfer. So the trauma surgeons and the anesthesiologists and the nurses—all of whom did an extraordinary job, really nothing short of heroic—they stabilized that patient, repaired the injuries that needed to be repaired, and that child is now en route to University of Chicago by helicopter to [Comer] Children's Hospital," Mark Talamonti, chair of Highland Park's department of surgery, said. (Molina, CBS News, 7/5; Tarm et al., Associated Press, 7/5; Sweet et al., Chicago Sun-Times, 7/4; Caldwell et al., CNN, 7/5)