(CBS News) CHICAGO - The sun is showing no mercy. The mercury soared again Thursday in the central and eastern United States, with temperatures in the 90s and over 100. The weather service put out a heat advisory for much of the region, including Illinois. The temperature in Chicago hit 103, breaking a record that had stood for more than a century.
And the heat wave may be aggravating a crime wave. There were 22 more shootings in Chicago overnight, five of them deadly. So far this year, the city has had 272 homicides. We take a look at crime in the heat of the night.
The victims of Chicago's increasingly bloody summer are trapped now between a plague of gangland violence and the onset of triple-digit heat.
Ten-year old Kitanna Peterson was out late Tuesday night on the far west side playing at a fire hydrant when she was shot. A stray bullet went through her wrist and abdomen.
"You know what kind of a man do that? A fool. But he'll be caught," said the girl's uncle, Homer Hardiman.
Many of the nearly two dozen wounded in the past 24 hours were -- like Kitanna -- outdoors and seeking relief from the scorching temperatures at what turns out to be exactly the wrong time of day. Statistically, 9 p.m. to 2 a.m. are the most murderous hours in this city's poorest neighborhoods where gangs thrive.
"Crime is unfortunately very concentrated in lowest income neighborhoods in the city," said Jenz Ludwig, who runs the University of Chicago crime lab. "Those are the neighborhoods where people are least likely to have air conditioning or adequate air conditioning."
The Chicago temperature reached 103 degrees Thursday afternoon. In fact, it's gone over 100 degrees for three straight days here. Researchers say that kind of heat triggers chemical changes in our bodies -- such as an increase in testosterone -- that can boost aggressiveness.
"That kind of problem is particularly dangerous in an environment when you have a lot of gangs and a lot of guns on the streets," said Ludwig.
Kitanna Peterson is in the hospital now recovering from her wounds. And on Thursday afternoon, a brief shower sent the thermometer down just a bit, providing some relief from the heat. But providing relief from the violence will require more than a few rain drops.