New pieces of information came up regarding the six sea lions shot dead in Columbia River traps.

According to The Associated Press, investigators think the killers managed to get through the tricky waters into the restricted area, dropped the doors of two metal cages and then began shooting with a high-powered rifle at the six trapped sea lions. They also reckon that, as the traps were close to an island, the killers arrived by boat.

Bob Lohn, regional administrator of the National Marine Fisheries Service, said that the people who did this must have been familiar with the traps.

“Suffice it to say that in order to undertake (the shootings) this person would have to be somewhat familiar with the trapping methods used there and the operation of the traps.”

Although veterinarians examined their bodies on Monday, they couldn’t find any bullets, said Brian Gorman, a National Marine Fisheries Service spokesman.

The investigators had an earlier theory which said that the gunshots were fired from the Washington side of the river, about 500 yards away, but they reconsidered it because of the closed cage doors. Normally the doors are left open so that the sea lions get used to the cage until trappers come to remove them, added Gorman.

The trapping started April 24 as the government gave Washington and Oregon permission to capture or kill up to 85 sea lions a year for five years because they fed on endangered salmon.

For now, sea lions trapping has been suspended until the investigations are over.