If that is the case then the aircraft could not be flown out without a complete inspection by a licensed engineer and the relevant authorisations.
There would also be no valid insurance.
The other point worth considering is where the aircraft is seized? In a bigger airport its likely there would be hangers and even maybe a licensed maintenance unit but if its seized on some small strip there maybe neither.
To move it from its seizure point to somewhere more suitable for the police to inspect it would put any evidence found in jeopardy of being used as evidence even if a police pilot flew it to an inspection site.
So I am sure you are right. Once on the ground the police will regard the aircraft not as an aircraft but as a piece of ground bound hardware which might contain evidence and to let anyone remove that hardware police or otherwise would give a good case that the evidence had been tampered with.
After the inspection it would then be up to a licensed engineer to certify the aircraft for flight again
Pace