Actually, all you need is the right jury, but you can still be nailed on civil charges:

Don't forget the incident in Louisiana where a Japanese student went to a costume party:
What I remember about it is that the homeowner's wife answered the door, got hysterical and yelled at her husband to "get the gun". What followed was a tragedy in anyone's lexicon:

What follows is stuff I cobbled together from a question and answer website:
_ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ _
?On October 17, 1992, Yoshihiro Hattori and Webb Haymaker were on
their way to a Halloween party for Japanese exchange students in a
quiet neighborhood in Baton Rouge, Louisiana. Arriving at the home
that they thought was the site of the party, they rang the doorbell
and waited. Because the front lawn of the modest brick ranchstyle home
was festively arrayed with Halloween decorations, they assumed that
they had found the right place. When no one appeared to answer the
door, they started back for the car in disappointment.?A Japanese exchange student, Yoshihiro Hattori, was searching for a
party he had been invited to. Thinking he had found the house in which
the social would take place, Yoshihiro knocked on the door. Not
knowing that they had the wrong house Yoshihiro and his companion
startled the proprietor. After having the front door shut in their
face the two boys began walking back to Yoshihiro's car. Yoshihiro
Hattori and his friend, Webb Haymaker, then turned back towards the
house upon hearing the carport door open behind them. Instead of
seeing the party's host, these two boys were greeted by a " 'Freeze' "
and a .44 Magnum-carrying Rodney Peairs. Yoshihiro, thinking he had
found the party after all, stepped towards Mr. Peairs and said, "
'We're here for the party' ". Webb Haymaker then found himself
standing over his dying friend, Yoshihiro Hattore, a victim of
unintentional homicide.?
?Yoshihiro Hattori, a 16-year-old foreign exchange student, was shot
in the chest in the carport of a Louisiana home, a place he had
mistaken for the site of a Halloween party he was to attend.
The homeowner, a man who had been raised on a part of the American
dream that the missionaries hadn?t mentioned, mistook the foreign
exchange student for an intruder.
When Yoshi Hattori failed to respond to the command "freeze!" - a
word he didn?t understand - Rodney Peairs pointed a .44-caliber Magnum
handgun at the student?s white John Travolta-style disco costume and
pulled the trigger.?

?In Baton Rouge, Rodney Peairs, the homeowner who gunned down Yoshi
Hattori, was indicted by a grand jury. He was charged with
manslaughter and put on trial in May. The jury, apprently convinced
that Peairs was well within his rights to blow away an inquiring
teenager, deliberated for just over three hours before acquitting
him.?

Yoshi's Gift Foundation

?On September 15, 1994, the parents of Yoshihiro Hattori won the civil
case with the amount of $653,000 as the compensation for damage
against Mr. Peairs who killed Yoshihiro by gun and his home owner's
insurance company. Out of $100,000 paid by the insurance company, the
Hattori received about $45,000 after the lawyer's fees and expenses
had been paid. The Hattoris created Yoshi's Gift from this money. The
Hattoris hope that, with the help of Yoshi's Gift, many gun control
groups will grow up and become stronger lobby groups against NRA.
Consulting with the Haymakers, Yoshi's host family in the US, the
Hattoris decided to establish the foundation. Yoshi's Gift was named
by Holley Haymaker, Yoshi's host mother.?