How to make these sentences passive: 'People believe that Jenkins is the culprit.' and 'People believed that Jenkins was the culprit.' [closed]

How to make these sentences passive? 'People believe that Jenkins was the culprit.' and 'People believed that Jenkins was the culprit.'

I know it is

Jenkins is believed to have been the culprit.

and

Jenkins was believed to be the culprit.

How come the same tense in the object clause 'that Jenkins was the culprit' becomes different infinitives – 'to have been' versus 'to be'?

It is to do with the time difference between the act and the belief.

When the crime occurred (in May 2005) Jenkins was believed to be the culprit.

Following a long investigation which lasted two years, in 2007 Jenkins was believed to have been the culprit.

More questions were raised by a 2009 investigation but following the recent discovery of further information Jenkins is (now) believed to have been the culprit.