The suspect in a Toronto van attack that killed 10 people and injured 15 others on Monday attended a high school program for students with special needs where he would often walk the halls with his head down and hands tightly clasped, according to former classmates.

 Suspect Alek Minassian, 25, was charged with 10 counts of murder and 13 counts of attempted murder in the incident.

One possible clue to his motive emerged on Tuesday as Facebook confirmed Minassian wrote a post before the incident that referenced an “incel rebellion.” The term is shorthand used in some online message boards for “involuntary celibacy”, a loose social media movement of men who blame women for their celibacy.

Canadian authorities have declined to say whether anger toward women had motivated the attack.

The post also voiced admiration for a man who killed six college students before taking his own life in California in 2014 and who cited the “cruelness of women” for his virgin status.