Does anyone know if CIC do any further checks or request for more information after the status is changed to DM? Or is it considered that the processing is now complete and we just have to wait for the ceremony invite.
Processing is ALMOST complete. A Decision is Made. For the vast, vast majority of citizenship applicants, DM means a Citizenship Officer has made a formal decision to grant citizenship (and if this is not true, those affected already know it, pursuant to the respective notice or communication otherwise, such as a fairness letter about a prohibition).
Thus, for the vast, vast majority of citizenship applicants, seeing DM means the next step will be scheduling the oath ceremony, then attending and taking the oath at the ceremony, and then actually, formally receiving the grant of citizenship.
THE CAVEAT for a SMALL, very small NUMBER of APPLICANTS:
BUT of course citizenship is NOT actually granted unless and until it is actually and formally granted to the applicant (who is technically a citizenship "
candidate" once there is a DM).
AND the candidate must remain eligible right up to actually taking the oath and being granted citizenship. Thus, for example, there is typically at least one more GCMS screening conducted before the oath, and the candidate is typically required to again affirm there are no situations which could possibly constitute a prohibition. Even if not formally asked, the applicant/candidate has an affirmative obligation to notify IRCC if there are any situations which could possibly constitute a prohibition.
For example, if the candidate is arrested for a domestic violence offence the night before the oath is scheduled, the candidate might be able to show up (if not incarcerated) at the oath ceremony and proceed to take the oath, assuming the final GCMS screening does not reveal the arrest (takes time for arrest records to be entered into the RCMP system and populate the databases which FOSS or GCMS will access). IT WOULD BE UTTERLY STUPID FOR THE CANDIDATE TO NOT DISCLOSE THE ARREST. Even though doing so will almost certainly mean NOT taking the oath.
It is imperative to disclose the arrest even if the candidate is certain of her innocence and certain the charge will be totally dismissed. Not only would a failure to disclose the arrest be a blatant misrepresentation by omission, it is currently the most likely kind of misrepresentation to be discovered sooner or later AND result in a proceeding to revoke citizenship, resulting in at least a TEN YEAR bar from citizenship and potentially real criminal prosecution.
If the candidate is arrested before taking the oath (driving while impaired is another all too common example tripping up citizenship applicants on the path to citizenship), the candidate absolutely should disclose this to IRCC. This means the candidate is prohibited. But it appears that in some cases IRCC merely suspends processing rather than immediately denying the application (to be clear, an arrest while the application is pending, even after a DM, constitutes a prohibition and is then grounds to deny the application). So, for the truly innocent candidate, there may be an opportunity to go to the Crown and Court and get the case dropped and then proceed through the process.
In any event, after DM there is usually at least one more GCMS screening (which includes FOSS).