Separate the fields before reconnecting them
A character may have a plausible motive or opportunity while the proposed method remains unsupported. Write the identity claim and the method claim separately, then identify the evidence connecting that person to that action. This prevents a strong impression about one field from filling gaps in another. The complete theory should connect them, but the connection needs to be shown rather than assumed.
Worked example: possession and action
A fictional suspect owns an object relevant to your proposed method. Ownership alone does not establish use at the relevant time. The object may have been lent, stored elsewhere or handled by another person if the records support such possibilities. Look for the documented relationship between the person, object and event instead of treating possession as a complete account of the action.
Review the bridge
For Somatry's report, ask which source supports the method and which source ties it to the killer. If both answers point only to the same vague suspicion, reread the relevant records. You do not need to invent technical details outside the file. A stronger report uses the method the case materials support and explains why the identified person is connected to it, rather than forcing an elaborate mechanism around a suspect chosen for unrelated reasons.