Connor MacCalister, the suspect charged in the fatal stabbing of a Saco woman in a supermarket Wednesday, had allegedly been planning the random attack for a month, documents revealed.

MacCalister, 31, of Saco, Maine, went to the store to kill "several random people" because he was "angry with life" and "wanted to get back at someone," Maine State Police Detective Kristopher Kennedy wrote in the complaint formally charging MacCalister with the murder of Wendy Boudreau, a 59-year-old mother and grandmother, according to the Portland Press Herald.

Police originally identified MacCalister as a woman, but MacCalister's brother, Jeremy Hopkins, revealed that MacCalister is a female-to-male transgender and has identified as a man for more than a decade.

The alleged stabbing took place after MacCalister followed Boudreau from the parking lot of the Shaw's supermarket into the ice cream isle, grabbed Boudreau from behind and slit her throat, according to NBC's Portland affiliate WCSH 6.

A Shaw's employee who was working in the bakery department responded to the scene when she heard screaming, only to find MacCalister standing over Boudreau, who was sitting on the floor, slumped over.

When the witness asked MacCalister the reason for the attack, the suspect responded, "She looked at me funny." Another witness told police that MacCalister told him: "I'm off my meds and I didn't mean to do it," the Maine Sun Journal reported.

Boudreau was rushed by paramedics to a local hospital where she died from her injuries.

MacCalister is being held at York County Jail and is expected to make a court appearance on Friday.