Since 2012rcampion does a good job (IMHO) covering the biometric side, I'll remind you not to overlook the obvious weaknesses not directly related to biometrics. These could still be used to break biometric security.
Back end
In a biometric system the data the biometrics is compared to is in a database as are the access rights the recognized user will get. The security of a biometric system can't be better than the security of that back-end. And the back-end needs access for administration, maintenance, and backups. And while those would presumably have high security levels it might be lower than for a vault or area a burglar tries to get in.
Hacking the administration would allow adding a new user you can match, adding access rights to user you can match, or changing biometric data of an existing user. Ability to perform a maintenance update might allow adding a back door that makes all locks open to a scan test device. Such test mode might already exist in the code and be available for use by editing some settings. The system might in general have testing, debug, or maintenance modes available.
Access to a backup, which presumably would be stored off-site, and thus might have lower security or need a data transfer that can be intercepted, might give you access to all the data you need to fool the biometrics. Presumably the biometric data would be securely hashed to prevent this, but the hashing function used might have a known flaw. Since performing updates might itself be a security risk, old code might live for a long time. And old backups might still be available with even lower security and obsolete hashing functions. And the biometric data would still be valid. Reminding users that the security system has been updated and they should change their DNA doesn't really work... Neither does telling people to use different DNA on different systems, so you can compromise an entirely different lower security system and have access to biometrics valid on a high security site.
People
Make somebody who has access do what you want. Realistically this would be used to bribe a systems administrator or head of security to tamper with the database. But if you have the bank managers family at a secure location with nasty people with knives, you can have access to anything the manager has access to. The same goes for the actual owner of the thing you are trying to steal, if it has one.
I doubt these examples are of direct use to you, but the general concept of dealing with a secure system by committing other crimes to make it less secure is a long tradition in fiction and should not be ignored.