Conversation so far:
When was Erich Mielke imprisoned?
On 7 December 1989, Erich Mielke was arrested and placed in solitary confinement.
What crime was Erich Mielke convicted of?
After twenty months of one-and-a-half hour daily sessions, Erich Mielke was convicted on two counts of murder and one of attempted murder.

Question: How long was Mielke imprisoned?
Self-contained rewrite: How long was Erich Mielke imprisoned in total?