Yes, he was probably suicided, but...
... it's impossible to know for sure. If politics is involved, police investigation is irrelevant.
Probably the most infamous example of "suiciding" I'm aware of is Roberto Calvi: Hanged under the bridge, clothes stuffed with bricks, injuries to his neck were inconsistent with hanging, and he had not touched the bricks found in his pockets. Yet, authorities stubbornly insisted it was a suicide.