Suspicious terrorist commited suicide in german prison

 Yesterday a suspicious terrorist was found dead in his cell in german prison. According to the police the men commited suicide. 

The 22 year old man was arressted just a few days before from german special forces. In his flat police found materials for a bomb. He was also suspected to have contacts to ISIS. Refugees who were living with him, called the police and helped to arrest him. The case was widely discussed in german media. 

Now, just a few days later he wa found dead in his cell. A chief witness is dying in supervision of police. How can this be? Politicians explain to us they need to have broughter access to email and mobile data for the fight against terrorism. What do they want with these datas, when they are not even able to protect the most important source of information sitting in their own prisons? I don't understand this!