Complex sentence: He was believed to have been killed by Soviet agents in the Pyrenees in 1937, after a series of unsuccessful attempts on his life; but according to the 1997 memoir attributed to Pavel Sudoplatov, Судоплатов Павел Анатольевич.
Split into simpler sentences: He was believed to have been killed by Soviet agents in the Pyrenees in 1937, after a series of unsuccessful attempts on his life. However, according to the 1997 memoir attributed to Pavel Sudoplatov, Судоплатов Павел Анатольевич.