Donald Trump Warns Nancy Guthrie Abductors Will Face Death Penalty If She Dies

Donald Trump is making it crystal clear ... if Nancy Guthrie’s kidnappers don’t bring her back alive, they could be staring down the ultimate punishment: the death penalty.

The President told the New York Post in a phone call the abductors need to release Nancy unharmed ... warning if she’s found dead, they’ll face "very, very severe -- the most severe" federal consequences.

When pressed on whether that meant the death penalty, Trump didn’t hesitate ... replying, "The most, yeah... that’s true."

Trump’s comments come after he personally called Nancy’s daughter, Savannah, on Feb. 4 to offer federal help ... with the investigation ramping up following the release of doorbell footage showing a masked intruder lurking outside Nancy’s home before she was taken against her will on Feb. 1.

The FBI also revealed DNA was recovered from a glove found about a mile away from the scene -- the gloves appears to visually match the gloves worn by the suspected kidnapper seen on the video. The DNA has been sent to a lab to be analyzed.

Meanwhile, TMZ continues to receive disturbing messages tied to the case ... including a fourth email Monday from someone claiming to know exactly who took Nancy and where she is.

The sender -- using the same bitcoin account as before -- wrote in part, "I know what I saw 5 days ago south of the border and I was told to shut up so I know who he is and that was definitely Nancy with them." He is demanding $50,000 in bitcoin upfront in exchange for the information.