It's an episode of Dragnet 1967 with Jack Webb and Harry Morgan. No need to watch the whole thing, although it's enjoyable to scroll through. As for the plot line -- well, you can see the premise (and the reason for posting this) from the image below.
It all starts when explosives are stolen from a warehouse, and Joe Friday and Bill Gannon go to investigate. Along they way, they come across a witness who had confronted the perpetrator in a car accident and got shot in the arm. It turns out there hadn't been an argument, but the reason for the shooting, as the on-site officer explains, "is because he said he was a Negro." Eventually, Joe and Bill track the suspect down to his home where its full of dynamite, guns and Nazi paraphernalia -- all intended to blow up a school...that was going to be integrated. And yes, happily, they stop the plot.
My favorite line comes at the very end, in fact the last line before the Epilogue, and it's 100% pure Joe Friday. The neo-Nazi clearly has no intention of doing any more talking, after gloating about how he knows his rights and that Friday will want a motive. Joe jumps right in -- "Hate'll do for a start. And try to put that walnut-size brain of yours to work on this. You keep harping about minorities." (The guy says, "That's right.") "Well, mister, you're a psycho. And they're a minority, too."
Cue the music. And then the narrator....
"The story you have seen is true..."