I reported this to my bank as soon as I found out, and Chase said that the money would be reimbursed once they completed their investigation (within 10 business days).
Chase was likely indicating that the money will be reimbursed within 10 business days of completing their investigation; not 10 business days from the date you told the that someone forged checks on your account. This would make sense when you think about it, as they need to make sure that you were not complicit in the crime (you would be surprised how many people have had someone cash multiple checks from their account only to split the money with them and file a claim for fraudulent transfer/forgery). Further, checks are a negotiable instrument, unlike a credit/debit card, where specific protections exist pursuant to its terms and conditions of use. You have a duty to keep a negotiable instrument safe, and while most banks will reimburse you if it can be established that you had no involvement and you were not grossly negligent in the keeping of the instruments, it is a different animal in and of itself.
It has now been 13 business days, and I have checked on the status twice and was told both times that there had been no status update, and they were unable to provide an updated ETA.
Unless your bank indicated in the disclosures of the checking account application and acceptance documentation that in the event of a stolen check you will be reimbursed in X amount of days, they have the absolute right to complete their investigation before reimbursing any funds to your account.
It's a fairly large amount of money, and I need to get it back as soon as possible. I'm trying to figure out if I have legal footing here. Does the law protect me from this type of fraud? And if so, does it require the bank to respond within any particular timeframe?
Federal banking regulations provide broad protections to consumers when it comes to fraud involving credit/debit cards, as these are easily stolen from all sorts of means. That said, checks do not carry the same protections, although oftentimes some. National banks may be required to reimburse customers for forged checks. However, based on individual circumstances, the bank can investigate to determine if the customer is entitled to a reimbursement. There is not duty to reimburse until the investigation is complete. This is why I think you've potentially misconstrued what they said about how long it would take. They cannot promise a time certain when they don't know how long the investigation will take.
Whether the bank is liable for the customer's loss depends on the specific circumstances of the case. Generally, a bank is liable for accepting a check that has been forged, altered, or improperly endorsed. However, if the bank can prove two things — that it accepted the check in good faith and exercised ordinary care and diligence in handling the transaction — it may not be liable.
If your actions — the way the check or checkbook was handled, issued, completed, or made payable — contributed to the making of the forgery, you may be at least partially liable. Generally, the bank will require you to complete an affidavit. It may also request that you file a police report.
** Addition: I forgot to mention that if the checks were not "cashed" (i.e. filled out to cash or cashed in person), but rather were presented to a 3rd party for payment in receipt of goods or services, you are also going to need to contact those individuals or businesses (their name is on the check) and alert them to the fraud, and allow them to contact their banks, lest you will be assessed fees by them for insufficient funds if your bank later takes the money back as a result of the investigation.
Also, in the event the checks were recreated rather than stolen, or if you don't know exactly how many were stolen, you are going to need to close your account while you wait for the investigation to bear fruit (hopefully), and open a new account, as you now have a duty to account for any and all checks stolen at that event (so, if you know a book is out there and 10 checks have cleared you know there are 15 remaining that the bank is not going to cover if you don't take steps to protect yourself). One would think they've asked you this and have already done something to prevent further checks from coming in, but if not, you need to get on it. Also, you may want to hire your own investigator if you have the funds to do so. While stolen cards are often strangers, stolen checks (unless it's one washed check) is nearly always someone you know.