Rex Heuermann -- the alleged Gilgo Beach serial killer -- has just been hit with a new murder charge ... an expected development, officially rounding out the 4 known victims.
Prosecutors lodged a new murder complaint against Heuermann Tuesday -- accusing him of killing Maureen Brainard-Barnes ... a woman who's long been tied to the Gilgo Beach case, but is now being connected to RH via law enforcement.
Maureen disappeared in 2007, and her remains were found in 2010. She was technically the first of the Gilgo Four that was discovered within days of each other -- with the other three women being Megan Waterman, Amber Costello and Melissa Barthelemy.
Heuermann had already been charged in connection to their murders ... and now, he's being rung up for Brainard-Barnes too -- mind you, there are outstanding women's disappearances that are currently being investigated that may well end up being linked to this.
The added murder charge for Brainard-Barnes was something that seemed to be coming -- investigators were waiting for DNA test results from hair recovered from her remains.
Now, it appears as though they feel they have enough evidence to point the finger. Heuermann has pled not guilty to the charges against him ... he'll have to answer for this one at some point down the line.
His defense lawyers thus far cast doubt on the DNA testing being conducted -- arguing the tech is faulty ... and that it doesn't provide a smoking gun, but simply eliminates other possibilities. Basically, they're saying cops have falsely landed on him as being their guy.