Alan Jackson Says He Wants to Rejoin Nick Reiner's Case as His Defense

Alan Jackson's down to jump back on the case as Nick Reiner's lawyer ... but there's a financial holdup ... and he tells us that's why Nick's petitioning for access to his trust fund money.

The famed defense lawyer joined us on "TMZ Live" Tuesday after Nick asked the court to give him the money he says he's owed from the trust fund Rob and Michele Reiner set up for him and his siblings.

Alan said it's "wildly unfair" that the money is being held back from Nick, because it's the trustee's duty to make sure Nick gets his payout. He noted ... "That is Nick's money."

According to the court docs, Nick says he never got the payout he should've received when he turned 30, even though he's 32 now ... and we asked Alan why that's the case.

If the financials can be worked out, Alan says he and his team are ready, willing and able to get right back to securing Nick's defense in his double murder case.

Alan explained he didn't want to leave the case in January ... and he said he had to bite his tongue as folks were speculating on why he bowed out.

He says things were never as black-and-white as some folks believed.

As you know ... Nick's awaiting trial for murdering his parents, after allegedly stabbing them to death in December, and he's currently repped by a public defender.

Alan seemed to be preparing a not guilty by reason of insanity defense when he was on the case ... and we asked him if that would be the plan if he comes back into the fold.