How do lawyers get paid in big murder trials?

Jodi Arias's attorneys were court-appointed, i.e., paid through state funds (I believe). There are also public defenders (licensed attorneys) for indigent people. Jodi Arias's attorney, Kurt Nurmi, started as a public defender then quit his job to get away from Arias. The judge said you have to keep her as a client.

Erik Menendez ran out of money to pay Leslie Abramson (for the retrial). They asked the judge if she could be court-appointed (reduced fee); judge said no. That was kind of BS, IMO. I do believe that Erik Menendez used all his money on the first trial.

"Expensive criminal case" depends on the judge and your jurisdiction, I think. You would have to ask the court to pay for experts, etc. If it's a complicated case, you would ask the court for a second attorney (like Jodi Arias had 2 attorneys).

If you’re not represented by a public defender, you need to hire a private criminal defense attorney. Usually you pay a retainer and then you pay costs billed on something like a monthly or biweekly basis. Traditionally, those bills are based on an hourly fee you pay for each lawyer who works on your case—so that might include junior attorneys doing the scut work in addition to the big shot you’re doing to deploy in court. More commonly now, the bill might be based on a lump sum per month that you negotiate at the beginning rather than hourly charges.

For costs other than the lawyers’ time and expenses (travel, hotel, etc), the lawyer usually checks with you first. This could include the cost of preparing exhibits or hiring an expert to testify in your defense. If you agree, that would then be added to the bill.

It is very difficult for a lawyer to dump a client, but one of the situations in which it’s allowed is if the client stops paying his bill. If you get your monthly bill and don’t pay it, your defense will come to an immediate halt and you may find yourself dumped onto a public defender’s desk. Of course, there are ethical lawyers in this world who would rather keep fighting for you and stack up your unpaid bills instead, but those kind of people don’t tend to become high-priced criminal defense attorneys.

Pro boner work.

Some defense attorneys take on these cases to promote their brand.

For a murder trial, most people would be bankrupted if they had to retain their own attorney and pay that attorney out of pocket.

Robert Shapiro said (and I believe him) that OJ Simpson still owes him money.

R5.

[quote] If you get your monthly bill and don’t pay it, your defense will come to an immediate halt and you may find yourself dumped onto a public defender’s desk.

You still need the judge's permission to withdraw. You can't always get it. Depends on how close to trial you are. I've seen judges in criminal NOT allow an attorney to withdraw if the client was detained and a new attorney would mean a continuance forcing the client to stay in jail longer. Usually if the retainer agreement was written advantageously to the attorney, the court may decide the attorney has already made enough on the case. Where I am if the money runs out then the court can appoint that attorney at court-appointed at the court appointed fees and the court then starts to pay for other legal services like investigators, experts, forensics, etc.

Attorneys usually know upfront what kind of resources are available for fees. They may take a lien on the parents' or grandma's house.