Possible Motive: Killing Ex-Wife

Investigators are becoming increasingly convinced that Beltway sniper suspect John Allen Muhammad went on his rampage because he planned to murder his ex-wife in what would appear to be a random slaying by a psycho spree killer, cops said.

Muhammad's second ex, Mildred Green, lives in Clinton, Md., 15 miles southeast of Washington -- which is why cops believe he chose the capital and its suburbs as his killing ground.

They believe he planned to terrorize the area with random sniper attacks, then shoot Green.

Police task-force investigators said they've all but eliminated terrorist ties or political ideologies as a motive, and believe the rampage was sparked by Muhammad's increasing anger at Green after their marriage failed and she won custody of their three kids.

Muhammad's first wife, Carol Williams, suggested this during a TV interview, saying, "I think he was in Maryland for his second wife."

Green's brother, Charles, was more direct, telling The Sun of Baltimore he was sure Muhammad had traveled from Washington state to kill Mildred because she had taken his kids.

Investigators said there's no evidence Muhammad contacted Green.

But sources said Green's neighbors reported seeing him parked near her home, and they theorize he was checking out her movements -- possibly in preparation for a sniper attack.

Sources added that the murder last February of a Tacoma, Wash., woman -- whose aunt helped Green in her bitter custody battle with Muhammad -- may have been an early sign of his homicidal feelings toward his ex.

The gun used in that slaying has been tied to Muhammad and his teen cohort, John Lee Malvo.