A jury has found three members of an Afghanistan-born Montreal family guilty of killing three daughters and a co-wife in a so-called honour killing.

Mohammad Shafia, 58, his wife Tooba Yahya, 42, and their son Hamed, 21, have been found guilty of four counts each of first-degree murder.

They have been convicted of killing Shafia sisters Zainab, 19, Sahar, 17, and Geeti, 13, as well as Rona Amir Mohammad, 52, their father's childless first wife in a polygamous marriage.

Their bodies were found June 30, 2009, in a car submerged in a canal in Kingston, Ont., where the family had stopped for the night on their way home from Niagara Falls, Ont.

The Crown theory was that Shafia, Yahya and Hamed drowned the four victims elsewhere on the site, placed their bodies in the car, then pushed it into the canal with the family's other vehicle.

The defence had said it was an accident, that they had gone for a joy ride with Zainab driving and accidentally plunged into the canal with Hamed watching, although he didn't call police.