abc Black 1 seems like a key point. After Black 3, a and b are mia to prevent an eye on the left. After Black 5 c and d are mia. If White plays 4 elsewhere then Black 4 will only allow for a single eye space.
If if White plays at 2 the best I can see is ko. Here:
And White 3 doesn't work because 4 will create a second eye on the left.
emeraldemon: What if black plays this way? it seems to kill. White can't keep black from connecting on the bottom. If this works there's no ko.