The correct answer is option 'C' - Jackson and Stephens.

The given question is asking about who checked the cell thoroughly. Let's analyze the options to understand why option 'C' is the correct answer.

a) The police:
- The police are generally responsible for investigating crimes and maintaining law and order.
- While the police may have been involved in the initial investigation of the cell, it does not necessarily mean that they thoroughly checked it.
- The question specifically asks about who checked the cell thoroughly, and it cannot be assumed that the police did so.

b) The Governor:
- The Governor is a political position and is typically not involved in the detailed investigation of crimes or checking cells.
- It is unlikely that the Governor would personally be involved in checking a cell thoroughly.

c) Jackson and Stephens:
- Jackson and Stephens are mentioned in the question but not much information is provided about them.
- However, since they are specifically mentioned, it can be inferred that they are the ones who checked the cell thoroughly.
- It could be possible that Jackson and Stephens are investigators or individuals assigned to examine the cell in detail.

d) Stephens:
- Stephens is mentioned in the question, but there is no information provided about who Stephens is or their role in the context of checking the cell.
- Without any additional information, it cannot be concluded that Stephens checked the cell thoroughly.

Conclusion:
Based on the information provided, option 'C' - Jackson and Stephens appears to be the most logical choice for who checked the cell thoroughly. However, it is important to note that without further context or information, it is difficult to provide a definitive answer.