From the declassified documents obtained by Canadian journalist, Stanley Tromp: http://www3.telus.net/index100/records2
from 26 December 1989, US Embassy Bucharest

Another explanation is that the immediate execution might help to take the wind out of the sails of the remaining groups of Securitate terrorizing the country, but we suspect that most of these are now fighting for sheer survival, rather than loyalty to Ceausescu.
[Note here: the issue/the question is not who was shooting, but why the Securitate were terrorizing the country. The fact that the identity of the terrorists was not in doubt by Embassy Bucharest personnel is significant and telling.]

…This will not, of course, solve the current terrorist problems posted by the renegade “Unitati Speciale de Lupta Anti-terrorista [sic.]” (USLA), the well trained “anti-terrorist” units which continue to maraud about brazenly.
[It is unclear here if the reference is to USLA from the Securitate who did not join the Revolution, or of elements of the USLA, who did not join the Revolution…but what is clear is that the Securitate, and elements of USLA, were considered responsible for the bloodshed.]