It wasn’t Professor Plum in the conservatory with the candlestick. So who — or, more accurately, what — killed as many as 300 people in Brazil’s Amazon River in 1981?

In Sunday night’s episode of “River Monsters,” fresh-water detective (and extreme angler) Jeremy Wade tackles the monumental task of narrowing down the suspects in this real-life game of Clue.

The capsizing of the riverboat Sobral Santos II in 1981 was one of the worst maritime disasters in the Amazon’s history, resulting in a tremendous loss of life and earning the nickname “The Amazon Apocalypse.” Since it occurred before DNA testing, hundreds of dismembered bodies and body parts pulled from the river were never identified.

In Sunday’s episode, Wade travels to the port town of Obidos, the scene of the horrific tragedy, to uncover what answers may lurk in the deep murky waters.

Although the official loss of life can not be confirmed, since records only need to be kept for 10 years, published reports following the event said that only about 180 people survived among the estimated 500 passengers on board the Sobral Santos II — which was overcrowded with excess cargo when it crashed into an unlighted dock.

Even though the accident occurred 33 years ago, it’s still fresh in the minds of the residents of the small Brazilian town — and after speaking with eyewitnesses from that night, Wade is able to come up with quite a list of possible suspects.

As always, Wade gets a line in the water to narrow down what was responsible for the carnage.

With so many fish species living in the Amazon, the list of contenders is long — including the chomping Pirarara, known as the Amazon redtail catfish.

But it would take several big predators — or even more, smaller predators — to be responsible for the carnage that ensued after the boat sank.

Reports at the time blamed man-eating piranhas, but Wade has doubts that they are solely, if at all, to blame for the initial attacks that dragged so many under the water, never to be seen again.

Sunday’s special two-hour season premiere — during which fans can submit questions on Facebook and Twitter — starts at 9 p.m., followed by Animal Planet’s first-ever live aftershow, which starts at 11 p.m. and will continue online at animalplanet.com from 11:30 p.m.-midnight with host Lisa Lucas.