I'd be careful about placing too much trust in this friend. If he'd knowingly rip off another grower, without so much as an afterthought, he'd possibly try and get you as well.

Also, let's just hypothesize for a moment. This guy has shown total disregard for the efforts of another grower, and had the foresight to keep his little secret from you while he was trying to get rid of it. This shows very little maturity on his part. Now, let's imagine that old dude gets busted with the remaining quarter pound that he's sitting on. Four ounces can land a person quite a bit of jail time, especially if it appears that there's intent to distribute.

...are you sure he wouldn't roll over on you and your crop, just to shave a couple of years off of his jail sentence? I've known of some "friends" who have done this to other friends when the fuzz caught up to them and threatened them with federal penalties.

Just bear this in mind, because as you should definitely know, unless this dude is taking active part in the upkeep of your crop, he really shouldn't even know anything about it in the first place.

You can never be too careful.