The age of consent in OK is 16 the man was the girls boy friend and most likely was invited in and had been invited there several times before.
Being invited does not make you an intruder having a daughter that likes men does not give you the right to shoot said men.
The mother over reacted, I have seen this before mothers who can not believe their girls are sexually active and want to put all the blame on the man.
The linked article doesn't give any details of the relationship between the 31 year old "man" and the 16 year old girl other than the man was found in the girl's bedroom. Taking the clearly desired inference that there was an intimate, but consensual relationship....
Any "man" mature enough to be sweating up the sheets with his girlfriend, ought to have the good sense to consider on what kind of reception he might get at his girlfriend's home, especially late at night, or early in the morning before visitors might be expected. A little basic decency and respect for the girl's parents, the homeowners, would suggest that short of an open invitation to bump fuzzies in the girl's bed, the "man" ought to be finding a different location for their "dates". This is not to suggest any kind of license to shoot older men sleeping with our daughters. But Heinlein's quote about an armed society being polite does seem to have some play here.
In most regards, the same things would apply to a 31 year old woman banging a 16 year boy. The one difference might be the degree to which the female presents a "reasonable man" fear of physical danger to the homeowner who discovers her in his or her child's bedroom.
Of course, whether the mom acted reasonably or illegally hinges or her state of mind. Did she know the man and shoot him out of anger or vengeance, knowing full well he posed no risk? Or was the man unknown to her such that she might have reasonably believed he posed a danger to her daughter, the other younger child in the home, and/or herself?
I believe the forum has previously discussed a case in which the daughter actually screamed "rape" (or something to that effect) when daddy caught her (unknown to dad) boyfriend in bed with her. In that case, the dad acted reasonably, while the daughter should have been charged with some kind of negligent homicide, at least.
This article is mute on these key points.
Charles