If it's the stock recovery (black screen with a red triangle) there's a trick to get the menu on that - power and volume up once you have that screen showing I think (it's been a long time).
This will erase all apps and data, but I'm afraid that if you don't know the gmail address and password there is no other way. If there were, then the lock would be useless as a security feature, because any thief could use that method to access all of the data on a stolen phone.