A 61-year-old Rochester man shot his granddaughter at the patio door of his home late Monday night, telling police he had armed himself with a pistol to investigate a suspected intruder, police said.

Authorities are still investigating the incident involving the 16-year-old girl, who lives at the house with her grandparents. Shot in the upper torso, she was taken to the hospital in critical condition but was expected to survive, Police Capt. Brian Winters said.

When the couple went to bed Monday night, the girl was at home, Winters said. When they woke to a noise outside around 11 p.m., the man got a 9 mm pistol and went to investigate while the grandmother called police.

The man saw a figure at the patio door and fired two rounds, striking his granddaughter once, Winters said. He declined to give the family's name.

The shot was fired from inside the residence to the outside, Winters said, declining to say whether it went through the door or if the door was open at the time.

"This is a tragic event and both the grandfather and grandmother were distraught and emotionally upset," he said.

As part of their investigation, police are waiting to speak to the girl, who was responsive but not verbal, Winters said. There was no evidence of a dispute or disagreement between the girl and her grandparents Monday evening, he added, saying she had been living with the grandparents for several weeks or months.

"She resides at the residence with her grandparents, so she was not breaking into the residence at all," Winters said. "Preliminary indications are that she perhaps left the residence to go outside and get some air and have a cigarette."

The grandfather, who serves as a pastor at a local church, was not arrested, but authorities will continue to investigate and, if appropriate, will forward the case to prosecutors for potential criminal charges, Winters said.

A phone call to the Rochester house, in the 2400 block of East River Road NE., went unanswered Tuesday.

The case comes just weeks after a man in Little Falls, Minn., was charged with fatally shooting two teenage intruders inside his home on Thanksgiving. Authorities in that case described the incident as an execution, with the shooter firing several times to finish off his victims. They said the shooter's reaction went beyond the legal protections of Minnesota law that allows crime victims to use reasonable force to protect themselves and their property during a felony.

Instances in which a shooter mistakes a relative for an intruder are rare, said Joseph Olson, a law professor at Hamline University and president of the Gun Owners Civil Rights Alliance.

Under Minnesota law, he said, the defender can use his gun if he reasonably perceives that there is a threat, such as someone in the house committing a felony, or if he believes he is in danger of death or great bodily harm. "It's based on his reasonable perceptions and his reasonable judgment from those perceptions that shooting is necessary," Olson said.

Olson said he would need more information to understand what happened in the Rochester case.

"The law realizes that perfection is not possible in heart-beating situations, and so we need more to know whether this is a good instance of self-defense that turned out unfortunately, or whether it's not an instance of self-defense, in which case it could be an assault," Olson said.

"Oftentimes they don't charge when you shoot relatives because it just adds to the family misery," Olson added.

Pam Louwagie  612-673-7102