We understand from the case files that without zinc coffins, the deceased were not going to be flown out. I investigated a bit further and came to understand that zinc as a material is effective in delaying decay of a cadaver and it allows a typically wooden coffin to be hermetically sealed.
The record shows that the deceased were frozen solid and sewed into tarpaulins for aerial transport. They were later to be thawed and forensically examined.
It occurs to me that sealing a body in a zinc coffin only to open it up again might ruin the integrity of the coffin. Secondly, the zinc coffin was not specifically required for any suspected radiation contamination. Third. a zinc coffin is used for people of some importance.
From this I conclude that there could be no surreptitious pre-flight re-dressing hard frozen corpses. Secondly, they were frozen and sewed so there was no real concern of a communicable disease escaping. Third, the DP9 were considered worth the expense and effort to be transported in something better than a utilitarian wooden casket, even though obtaining them was an inconvenience and a government expense.
I do not support the idea that using a zinc casket was a ploy to hide evidence of assassin's work. Far to many rescuers saw what they say, carried what they carried, and talked as they wished.
The DP9 (not 10 or 11) died by natural causes and moved in a military fashion which owing to the zinc caskets was not particularly expedient..