Complex sentence: In the interview, the two said that they were in the Veldzicht mental institution with De G. in the mid- 2000s and that during that time they heard De G. say he had strangled a girl.
Split into simpler sentences: In the interview, the two said that they were in the Veldzicht mental institution with De G in the mid- 2000s. They said that during that time together they heard De G. say he had strangled a girl.