Addendum: after watching an interesting YouTube video on the disaster, it seems that not filling the lifeboats actually wasn't all that incompetent. A lot of people didn't think the boat was really sinking, and there was another large ship
within visual distance which could see them and their flares, and which they were radioing for help, so they thought help was going to be there very shortly if they needed it. Unfortunately, there was some very serious incompetence going on at that ship: the radio operator had gone to sleep for the night, and the captain, despite seeing many flares, decided not to bother investigating. After the disaster, apparently his story changed every time he was asked.
Anyway, I think my point stands: trying to murder someone by engineering a disaster at sea like this is pretty ridiculous; too many things have to go wrong all at the same time, which really aren't under control of any one person or small group. Getting the captain to speed through iceberg territory (and honestly, there weren't that many icebergs, they were just unlucky and happened across a big one), making sure a large iceberg was directly ahead, making sure just enough compartments flooded, making sure the radio operator on the other ship went to bed, making sure the captain of the nearby ship refused to investigate, and finally when help did arrive (and it did), making sure the assassination target somehow wasn't among the survivors. Killing someone in a prison cell where there's no witnesses except a camera or two (that "just happened" to be "malfunctioning") and a couple of guards to bribe is actually realistic and possible, especially if state-level operatives are involved.