Experts: Iran's arrest of U.S. sailors broke international law
The matter of "innocent passage" is more complicated than a few lines of legal/treaty documents.
If we put down the legal technical part, this is what I understand of "innocent passage".
1. Party A transit Party B's territorial water from point a to point b both in international water.
2. The shortest route is of course a straight line which go through Party B's territorial water.
3. Party A has innocent passage if either the straight line is the only path, or more likely any alternative path (not passing territorial water) is significantly longer, impractical. This is the first thing subject to different understanding, not set in stone.
4. The passage must be transit in nature, no maneuver, no stop, and shortest path. There should be no action that indicate intension of hostility. This is the second thing subject to understanding of both parties, again not set in stone.
Now, if we put this incident in perspective. Iran and U.S. have a long history of hostility including casualties. Past confrontation is very fresh, so Iranian interpretation of intension of the passage would be to the hostile side regardless the true intension/reason of U.S. This defeat the 4th point of "innocent passage".
When the arrest happened, Iran has no information from US side claiming drift caused by human errors. That means, in Iranian eyes, it is a simple incursion. How could anybody know if the "intruding" boats are merely sailing through for a passage without communication? The only thing the Iranian see is a potential hostile party coming straight into their territorial water. Also, even the boat managed to sail away from Iranian water after realizing the mistake, that would make the move certainly an intended incursion than a passage because it is not straight through but rather maneuver. This defeat both point 3 and 4.
Claiming the right of "innocent passage" by one side is one thing, but who is to judge that act is really "innocent passage"? The difference of it with "invasion" is only of the intension, therein the trust of the two parties. In this case, there is no trust. I am sure if the boats drifted into Oman's water, there wouldn't be any problem at all.
If we put the case in a court just like domestic case, person A stepped on the foot of person B, person A claims accident, person B claims insult. The law says accident is forgivable but insult is punishable. Both A and B can be legally right or wrong, depending on how the Judge interprets. Now there is no Judge in the incident of Iran/U.S. So I fail to see how Iran broke international law more than U.S. did or not.
The "Expert" in that article has his right to make his opinion heard, just like the lawyer of person A of the domestic case above. But there is surely other expert holding different views and I am one of them. I use quotation marks for that "expert" is because he sounds like a lawyer than a neutral academian who acknowledge more than one possibilities.
Another thing is that, the quick release of the U.S. personnel actually indicated the communication was established very quickly after the incident and Iran has accepted the explanation, put aside the propaganda thing moves. This is a very positive development from both sides (the administration of both sides). But we also see the flame-fanner of both sides too.