Nick Reiner wants the money he says he's owed from the trust his parents Rob and Michele Reiner set up for him ... as he awaits trial for their murders.

According to court docs obtained by TMZ, the 32-year-old filed a petition Monday, requesting the distribution of money he says was supposed to be paid out from the trust when he turned 30.

Nick said he tried to hire lawyer Alan Jackson to help him fight the murder charges, which he says his siblings Jake and Romy agreed to. He claims the trustee refused to pay Jackson which caused him to depart the case.

According to the petition, Nick told the trustee "time is of the essence." He explained that he needed Jackson to avoid "further jeopardizing my defense in the criminal matter." He went on to say his efforts to get the money have been "met only with delay and inaction."

Nick is seeking accounting and damages from the trustee.

The papers say his parents set up the fund in 1992 for Nick, Jake, and Romy. The filing states that Nick currently has no other source of funding his legal fees or basic support while behind bars.

As you know, Nick has been charged with two counts of first-degree murder for allegedly stabbing his parents to death in December.

We broke the story ... in February we learned Romy and Jake have no plan to spring for a private lawyer for their brother after Jackson stepped down.

In April, his brother Jake shared a heartbreaking post about their killing -- just days ahead of Nick's preliminary hearing -- saying ... "I was robbed of so many things that day. My parents won't be at my wedding, they won't get to hold their future grandchild, and they won't get to see me have the successful career I'm still seeking."

Their sister, Romy, hasn't spoken publicly about the terrible tragedy, but Jake said in his post that she would "in her own way and in her time."

Nick has pleaded not guilty and appeared in court April 29 for the prelim ... where it was confirmed that Rob and Michele's autopsies still weren't done, 4 months after their tragic deaths.