The two Belgian brothers who blew themselves and 31 other people up in Brussels on Tuesday started out as carjackers and bank robbers before graduating to terrorism.

Investigators are racing to assemble a fuller portrait of Ibrahim and Khalid el-Bakraoui who — along with at least two accomplices — carried out the suicide attacks at Brussels Airport and a subway station.

Here is what is known about each man, based on public records, official announcements, and interviews with neighbors, lawyers and law enforcement officials.

Brussels Born and Raised

Ibrahim, 29, and Khalid, 27, grew up in Laeken, a working-class neighborhood in northwest Brussels, not far from the Royal Palace. Their father, a retired butcher, is a devout Muslim who emigrated from Morocco; their mother is conservative and reclusive. The brothers shared burly features, and, by their mid-20s, had amassed a formidable record of violent crime.