Robert Card might have been targeting his ex-girlfriend when he chose two specific locations in Maine to go on his alleged mass murder spree.
The U.S. Army Reservist used to hang out with his former lover at the bowling alley and bar and grill in Lewiston, where he unleashed his brutal attacks with an AR-style rifle, killing 18 people and injuring 13 others.
Law enforcement told ABC News ... Card's sister believes the shootings were triggered by a "domestic dispute," which police are now exploring as a possible motive. Card's family has reportedly been cooperating with investigators.
According to court docs ... Card was once married, but got divorced in 2007, and his ex-wife cited "irreconcilable differences" as the reason. The divorce order included shared custody of their son, who was then a minor and primarily living with his mother.
Before his alleged killing rampage, Card wrote a note and addressed it to his son, leaving it behind at his Bowdoin home, ABC said. Investigators later found the rambling "suicide note," containing personal information and bank account details.
In 2002, Card enlisted in the Army Reserve and became a petroleum supply specialist. He was responsible for receiving, storing and shipping petroleum-based products.
Recently, Card reported he was having mental health issues, including "hearing voices." Over the summer, he was committed to a mental institution for two weeks after he threatened to shoot up a military base in Saco, ME.