Complex sentence: The authorities organized what was then the largest manhunt in the history of the island and placed a US $10,000 bounty on his head, either dead or alive, which was a first in the crime annals of Puerto Rico.
Split into simpler sentences: The authorities organized what was then the largest manhunt in the history of the island. They placed a US $10,000 bounty on his head, either dead or alive, which was a first in the crime annals of Puerto Rico.