Cannot remove user from AD, access is denied

I'm trying to remove a user from our AD using Adsiedit but I get this error:

Operation failed. Error code: 0x5 Access is denied.
00000005: SecErr:DSID-031A1256, problem 4003
(INSUFF_ACCESS_RIGHTS), data 0

I removed all permissions, made myself owner and gave myself full permissions but still same error.

Somehow the user is messed up because it isn't visible in Users and Computers. When I check the account properties I also noticed that the sAMAccountType is 805306370 (TRUST_ACCOUNT).