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By one estimate, there are about 400,000 illegal immigrants now living in the Houston area.

How much are they adding to our crime rate?

After last month’s murder of Houston police Officer Rodney Johnson, 11 News found out more about it.

An officer buried, a controversy renewed

The killing of Officer Johnson last month has become a political issue.

KHOU-TV

Two men try to make it across the border.

The accused gunman was a Mexican citizen who’d once been deported but was back in Houston, apparently illegally.

It was the kind of crime that for months now, has been seen by some as reason to crackdown on undocumented immigrants in the city and at the border.

The murder of Officer Johnson came just weeks after Congress had held hearings in Houston.

County officials testified that jailing and prosecuting un-documented immigrants was costing tens of millions of dollars.

“Undocumented immigrants and violent crime in Houston: is there a connection. And if there is, is it one more reason to toughen security at the borders?” said one politician.

We found that in fact, there’ve been several studies done in Texas and other border states trying to answer that basic question: do immigrants raise crime rates?

Pia Orrenius is an economist with the Federal Reserve Bank.   We tracked her down in Dallas.

“No, no they’re not more crime prone. In fact, when you look at the national statistics, its just amazing. There’s not a single scientific study that shows immigrants are more likely to commit crime than native-born, in fact, or U.S. born,” she said.

She says past studies show young, immigrant Mexican men are substantially less likely to commit serious crimes than young men born here.

“The number of immigrants in a community cannot explain changes in crime rates or the level of crime rates and that’s been shown time and again,” said Orrenius.

She and a fellow researcher also did their own study of crime on the border where, in recent years, security has been greatly increased.

And what they found surprised them.

“Property crime rates fell faster on the border than they fell in the U.S. which was a surprise to us,” said Orrenius.

That’s right, where immigrants were illegally entering the country, property crime was dropping, fast.

But violent crime was another story. It dropped some but not as much.

Why?

The researchers traced it to, of all things, the effects of all that beefed-up security.

All those cameras and patrols are making it harder for illegal immigrants to cross, so they increasingly are using smugglers to help them.

Smugglers who years ago were called “guides”. 

“We don’t call them that anymore because they’re not guides. They’re more seasoned criminals. They increasingly work in organized crime syndicates,” Orrenius said.

Criminals, who can sometimes have the illegal immigrants carry drugs and involve them in other crimes where violence becomes more likely.

None of this may in any way explain what happened last month to Officer Johnson.

But some of those who study immigration say it’s wrong to assume that people who often come here with so little are therefore more likely to break the law, when just the opposite may be true.