BOSTON — Dzhokhar Tsarnaev’s lawyers may try to save him from the death penalty in the Boston Marathon bombing by arguing he fell under the murderous influence of his older brother, legal experts say.

The outlines of a possible defense came into focus this week when it was learned that Tsarnaev’s attorneys are trying to get access to investigative records implicating the now-dead brother in a grisly triple slaying committed in 2011.