The trap in that pic is 32 x 12 x 10. I think Howard E will be right that the weasel would be too small IF that's the size of the trap you were using. I buy a two trap package; the second trap is 24 x 7 x 7. The smaller trap works very well for trapping all sizes of rats. I haven't trapped a weasel, but that would be the more appropriate size. The weasel boxes Howard E speaks of appear to work very well.That's great trapping. We used this same trap to try to catch a weasel. Baited it with parts of the chicken that the weasel left behind. Only think we caught was a skunk!

A weasel may not be big enough to trip the trigger on the havahart live trap....or at least one of that size.
If you think he is still a problem, try making yourself a weasel box and use a Victor wooden rat trap.
About 1,000 how-to videos for weasel boxes on youtube.