Looks similar to Long-necked Seed Bug (Myodocha serripes) that I saw here in Michigan. Maybe try the same genus and search and look though the images or try BugGuide.

Good call, very likely Myodocha genus. Not either of the two in bugguide, and images of newly-described Jamaican species are hard to find.

Could it by chance be the Longlegged/Milkweed Assassin bug? They can be black as well.

All images I see of Zelus longipes - Milkweed Assassin Bug have considerable orange or red areas.

You are right, it is not the Milkweed Assassin Bug. However I have some doubts that this black bug is of the Myodocha genus since it does not have the two fat front legs which I observe in the photos of the Long-necked Seed bug, and as seen in the attached photo . . . this bug has spikes.

True about the enlarged forelegs; but I cannot find a spiky Myodocha at bugguide; where is your image from?

We found this bug perched inside on the wall, one warm evening in Jamaica West Indies.

Try searching for family Rhyparochromidae, that generalizes the search a little more and you might find something closer to your "bug".

At bugguide, of the Rhyparochromidae, only Myodocha resembles the above images. I now think SuzAndy is on the right track with genus Zelus in the assassin bugs, the closest I can find is Z. tetracanthus, but yours is spinier.