Helaku can be seen during the mission "Great Men Are Not Always Wise", where he executes Baxter Deaton before other gang members rush out of the bank. He is then seen holding some civilians hostage in one of the rooms on the first floor of the bank. He is also encountered during the mission "At Home With Dutch", where he is acting as a scout for Dutch's Gang and must be neutralized by Marston in order to survey the camp.
Hey there, cowboy. It looks like this little ol' article is a bit puny. I reckon you could impress me by adding to it. Don't be shy now. If you're logged in, it'll help you earn them fancy achievements, too.