SOUTH BEND — Reports of violence over the last week in South Bend include attempted murder by arson and a series of weekend shootings. A new study confirms what police already knew: one potential reason for the increase in crime? Heat.

All three shootings occurred early Sunday morning, injuring three people including an 18-year-old girl and a six-year-old boy. They came on the heels of last month's shooting death of a 16-year-old Clay High School student on South Bend's west side, and are the latest cases in a string of violence involving teens over the last few weeks.

One Indiana criminal justice professor thinks "hot tempers" from hot weather may be at least partly to blame.

"Turn up the heat and humidity, add out of school teens, a sprinkle of tourists, and you have the perfect recipe for a long, hot summer of crime," wrote Ball State University Criminal Justice and Criminology Professor Dr. Jerry McKean in the crime statistics study, originally published in 1999, but recently updated. "It doesn't take much to push people over the edge."

You don't have to convince Sandra Vasquez of that. She's seen it happen just about every weekend for the last two months.

"Thursday, Friday, and Saturday night, it's a lot of cars. We can't even sleep," she said. "Most of the time it's teenagers. Some of them are as young as 13, 14, and 15 years old."

Lately, she says the crowds in her near northwest side neighborhood are almost always up to no good.

"[Monday] night, I heard gunshots, five gunshots," she said. "This was probably 11:30 at night."

It's not the first time.

Last spring, she awoke to find four bullet holes in the siding next to her front door. She also found another gunshot hole further up going straight through the wall of her son's bedroom.

"My brother in law was sleeping in there at the time. And it was this far from his head and from hitting him," she said, moving her fingers just a few inches apart.

It is frustrating and frightening, Vasquez said, particularly for her two young children.

It's also not the least bit surprising to McKean.

"The warmer months, starting in late spring and into the hottest part of the summer is the time we begin to see a peak in crime rates, particularly in property crimes, but to some extent for violent crimes as well," McKean told WSBT by phone from Ball State's campus in Muncie.

The statistics show it.

According to the FBI's annual crime report, violent crimes like murder and assault spike in July and August. So do property crimes like burglary and larceny.

Statistics from an FBI crime report in 1997 included in McKean's study show 18.4% of all crimes in the U.S. were committed in July and August. Compare that with a cold weather month like February, when just 7.2% of the year's total crimes were committed.

Preliminary FBI crime statistics for 2008 also show a slight increase in violent crimes in South Bend, up from 805 total cases in 2007 to 819 total cases in 2008.

That includes more than double the number of murders, as well as smaller increases in forcible rapes and aggravated assaults. Property crimes were also up in South Bend from 2007 to 2008, as were burglaries and motor vehicle thefts, according to the FBI report.

Robberies, larceny-thefts and arson cases, however, were sharply down.

McKean has several theories for why, including the weather itself.

"That can be largely anecdotal. But those folks that live in lower socio-economic areas without air conditioning, well, the sensible thing to do is to go outside and catch the breeze. So, you have a lot more folks congregating in public areas," he said.

"There's actually a couple of centuries worth of research that suggests that, to some extent, crime increases as you go South toward the equator. People have been discussing why that would be the case for a long time, but essentially, the most obvious explanation is probably the most true: heat gets people aggravated," McKean continued.

FBI statistics, McKean added, have shown that correlation to be true for decades.

There is another theory, too. This time, involving exactly who is congregating.

"School is out for the summer, so you have a larger population of teenagers. And teenagers are both at high risk of offending and at high risk of being victims of crime. Schools are very, very safe places for adolescents to be, compared to being out in public areas. Their risk of criminal behavior and victimization increases the more they're out in unsupervised places, and summertime is when that happens," McKean said.

"We have a very strong correlation between when school is in and when school is out with our property crimes, especially larceny," agreed South Bend Police Captain Phil Trent. "When kids lose their structure and aren't in school and curfews start getting relaxed at home, you see these roving bands of kids that come out at night. And that's when they get into trouble."

And it's not just property crimes that tend to occur when that happens, Trent said.

"When kids are out after dark, just wandering around, they're going to get into trouble. And that can mean violent encounters as well," he said.

Police have a plan to fight back.

Using federal grant funding, they're already increasing patrols in higher crime areas during the summer months. Trent says they can't do it alone.

"We're asking for help with those precautions. Take control of your kids and add structure to their lives in the summertime when they're out of school. Because, that's where we're seeing these spikes," he said.

It's exactly what Vasquez is doing with her two children.

"We're only out playing in the daytime for a few hours when there's no one else around. Otherwise, I'm inside," she said.

Her hope now: that heated arguments brought on by heat waves break soon. Unfortunately, with temperatures forecast to approach 90 degrees later this week, South Bend Police acknowledge that may not happen.

That's why they'll be using a new federal violent crime grant to add even more patrols, hoping to put a damper on any hot tempers before they start.