De Anza Community College in Cupertino was spared a shooting incident in 2001 when a photo lab saw pictures of a young man posing with his stockpile of weapons. The disturbed man was hinting at his plot.
http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2001/01/31/MNDEANZAPM.DTL

Police say DeGuzman also created bombs, stockpiling them over the two years he allegedly planned the attack on the junior college where he was a second-year student. The alleged plan was discovered when DeGuzman took photos of his arsenal, police said, then had them developed at a Longs Drugs a few miles from his house.

The clerk who developed the photos was 18-year-old Kelly Ben nett, whose father is San Jose veteran patrolman Robert Bennett. Kelly Bennett said today that what she saw in the photos disturbed her: Molotov cocktails, pipe bombs, and a T-shirt printed with the words "Natural Selection."

This guy made it obvious. Bombs, stockpiles and pictures.

"Once I realized my class was scared, I knew I had to do something," she said......

"You can't make me." Giovanni said she appealed to [Professor] Roy, who then taught Cho one-on-one.

...Roy said she warned school officials.

But I don't think that a fair-minded reading of his one-act play would incline anyone to interpret the play as a warning sign.  The action is plainly modeled on Hamlet.  Now I know that Hamlet is about a young man who may be pretty scr***d-up.  But the young man in "McBeef" is much younger than we usually think of Hamlet today, and the action makes his accusations about the father being murdered seem almost completely unfounded.

The last action is "(Out of sheer desecrated hurt and anger, Richard lifts his large arms and swings a deadly blow at the thirteen year old boy.)"  The extreme accusations that the boy has hurled at Richard have turned Sue against Richard in an instant, without a chance for Richard to say a word in his own defense.  

The reference to Richard's "hurt" is in fact inconsistent with Richard being a pedophile.  I can't say how Cho meant the reference, but "desecrated" could have been an attempt to describe the hurt and anger as frustration or as an angry response to an unjust accusation.

In other words, my first impression of this one-act tragedy is that Cho set up a conflict in which the boy's hurt and anger at losing his father results in verbal aggression against Richard; that that verbal aggression is so hurtful to Richard that he strikes back in frustration, with tragic and unintended consequences.  Richard seems to be the victim, and his fatal blow to be a tragic mistake.

The boy's remarks about "father not being good enough for my mother" may be some of Cho's own emotions about his own parents -- those remarks certainly don't have any analogue in Hamlet.  Who knows?

Discussions of Cho can only lose credibility from relying on cursory references to this play.  The poems may or may not be more disturbing, and may have justified the counseling referral, but my own experience is that many school administrators tend to over-react to some unusual behaviors and to miss the significance of true warning signs.

She said that was worried that Mr. Cho could be a threat to other students as well as to himself.

"I really felt very strongly that he was suicidal, that he was so depressed that he had a negativity about him, like it was like talking to a hole sometimes, that the person wasn't really there," she said.

"Of course, we never imagined these kinds of things."

After Columbine, how could someone not imagine something like this?